log_processor.rs

//! # OpenTelemetry Log Processor Interface
//!
//! The `LogProcessor` interface provides hooks for log record processing and
//! exporting. Log processors receive `LogRecord`s emitted by the SDK's
//! `Logger` and determine how these records are handled.
//!
//! Built-in log processors are responsible for converting logs to exportable
//! representations and passing them to configured exporters. They can be
//! registered directly with a `LoggerProvider`.
//!
//! ## Types of Log Processors
//!
//! - **SimpleLogProcessor**: Forwards log records to the exporter immediately
//!   after they are emitted. This processor is **synchronous** and is designed
//!   for debugging or testing purposes. It is **not suitable for production**
//!   environments due to its lack of batching, performance optimizations, or support
//!   for high-throughput scenarios.
//!
//! - **BatchLogProcessor**: Buffers log records and sends them to the exporter
//!   in batches. This processor is designed for **production use** in high-throughput
//!   applications and reduces the overhead of frequent exports by using a background
//!   thread for batch processing.
//!
//! ## Diagram
//!
//! ```ascii
//!   +-----+---------------+   +-----------------------+   +-------------------+
//!   |     |               |   |                       |   |                   |
//!   | SDK | Logger.emit() +---> (Simple)LogProcessor  +--->  LogExporter      |
//!   |     |               |   | (Batch)LogProcessor   +--->  (OTLPExporter)   |
//!   +-----+---------------+   +-----------------------+   +-------------------+
//! ```

use crate::{
    export::logs::{ExportResult, LogBatch, LogExporter},
    logs::{LogError, LogRecord, LogResult},
    Resource,
};
use std::sync::mpsc::{self, RecvTimeoutError, SyncSender};

#[cfg(feature = "spec_unstable_logs_enabled")]
use opentelemetry::logs::Severity;
use opentelemetry::{otel_debug, otel_error, otel_info, otel_warn, InstrumentationScope};

use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::{cmp::min, env, sync::Mutex};
use std::{
    fmt::{self, Debug, Formatter},
    str::FromStr,
    sync::Arc,
    thread,
    time::Duration,
    time::Instant,
};

/// Delay interval between two consecutive exports.
pub(crate) const OTEL_BLRP_SCHEDULE_DELAY: &str = "OTEL_BLRP_SCHEDULE_DELAY";
/// Default delay interval between two consecutive exports.
pub(crate) const OTEL_BLRP_SCHEDULE_DELAY_DEFAULT: u64 = 1_000;
/// Maximum allowed time to export data.
pub(crate) const OTEL_BLRP_EXPORT_TIMEOUT: &str = "OTEL_BLRP_EXPORT_TIMEOUT";
/// Default maximum allowed time to export data.
pub(crate) const OTEL_BLRP_EXPORT_TIMEOUT_DEFAULT: u64 = 30_000;
/// Maximum queue size.
pub(crate) const OTEL_BLRP_MAX_QUEUE_SIZE: &str = "OTEL_BLRP_MAX_QUEUE_SIZE";
/// Default maximum queue size.
pub(crate) const OTEL_BLRP_MAX_QUEUE_SIZE_DEFAULT: usize = 2_048;
/// Maximum batch size, must be less than or equal to OTEL_BLRP_MAX_QUEUE_SIZE.
pub(crate) const OTEL_BLRP_MAX_EXPORT_BATCH_SIZE: &str = "OTEL_BLRP_MAX_EXPORT_BATCH_SIZE";
/// Default maximum batch size.
pub(crate) const OTEL_BLRP_MAX_EXPORT_BATCH_SIZE_DEFAULT: usize = 512;

/// The interface for plugging into a [`Logger`].
///
/// [`Logger`]: crate::logs::Logger
pub trait LogProcessor: Send + Sync + Debug {
    /// Called when a log record is ready to processed and exported.
    ///
    /// This method receives a mutable reference to `LogRecord`. If the processor
    /// needs to handle the export asynchronously, it should clone the data to
    /// ensure it can be safely processed without lifetime issues. Any changes
    /// made to the log data in this method will be reflected in the next log
    /// processor in the chain.
    ///
    /// # Parameters
    /// - `record`: A mutable reference to `LogRecord` representing the log record.
    /// - `instrumentation`: The instrumentation scope associated with the log record.
    fn emit(&self, data: &mut LogRecord, instrumentation: &InstrumentationScope);
    /// Force the logs lying in the cache to be exported.
    fn force_flush(&self) -> LogResult<()>;
    /// Shuts down the processor.
    /// After shutdown returns the log processor should stop processing any logs.
    /// It's up to the implementation on when to drop the LogProcessor.
    fn shutdown(&self) -> LogResult<()>;
    #[cfg(feature = "spec_unstable_logs_enabled")]
    /// Check if logging is enabled
    fn event_enabled(&self, _level: Severity, _target: &str, _name: &str) -> bool {
        // By default, all logs are enabled
        true
    }

    /// Set the resource for the log processor.
    fn set_resource(&self, _resource: &Resource) {}
}

/// A [`LogProcessor`] designed for testing and debugging purpose, that immediately
/// exports log records as they are emitted.
/// ## Example
///
/// ### Using a SimpleLogProcessor
///
/// ```rust
/// use opentelemetry_sdk::logs::{SimpleLogProcessor, LoggerProvider};
/// use opentelemetry::global;
/// use opentelemetry_sdk::export::logs::LogExporter;
/// use opentelemetry_sdk::testing::logs::InMemoryLogExporter;
///
/// let exporter = InMemoryLogExporter::default(); // Replace with an actual exporter
/// let provider = LoggerProvider::builder()
///     .with_simple_exporter(exporter)
///     .build();
///
/// ```
#[derive(Debug)]
pub struct SimpleLogProcessor<T: LogExporter> {
    exporter: Mutex<T>,
    is_shutdown: AtomicBool,
}

impl<T: LogExporter> SimpleLogProcessor<T> {
    pub(crate) fn new(exporter: T) -> Self {
        SimpleLogProcessor {
            exporter: Mutex::new(exporter),
            is_shutdown: AtomicBool::new(false),
        }
    }
}

impl<T: LogExporter> LogProcessor for SimpleLogProcessor<T> {
    fn emit(&self, record: &mut LogRecord, instrumentation: &InstrumentationScope) {
        // noop after shutdown
        if self.is_shutdown.load(std::sync::atomic::Ordering::Relaxed) {
            // this is a warning, as the user is trying to log after the processor has been shutdown
            otel_warn!(
                name: "SimpleLogProcessor.Emit.ProcessorShutdown",
            );
            return;
        }

        let result = self
            .exporter
            .lock()
            .map_err(|_| LogError::MutexPoisoned("SimpleLogProcessor".into()))
            .and_then(|exporter| {
                let log_tuple = &[(record as &LogRecord, instrumentation)];
                futures_executor::block_on(exporter.export(LogBatch::new(log_tuple)))
            });
        // Handle errors with specific static names
        match result {
            Err(LogError::MutexPoisoned(_)) => {
                // logging as debug as this is not a user error
                otel_debug!(
                    name: "SimpleLogProcessor.Emit.MutexPoisoning",
                );
            }
            Err(err) => {
                otel_error!(
                    name: "SimpleLogProcessor.Emit.ExportError",
                    error = format!("{}",err)
                );
            }
            _ => {}
        }
    }

    fn force_flush(&self) -> LogResult<()> {
        Ok(())
    }

    fn shutdown(&self) -> LogResult<()> {
        self.is_shutdown
            .store(true, std::sync::atomic::Ordering::Relaxed);
        if let Ok(mut exporter) = self.exporter.lock() {
            exporter.shutdown();
            Ok(())
        } else {
            Err(LogError::MutexPoisoned("SimpleLogProcessor".into()))
        }
    }

    fn set_resource(&self, resource: &Resource) {
        if let Ok(mut exporter) = self.exporter.lock() {
            exporter.set_resource(resource);
        }
    }
}

/// Messages sent between application thread and batch log processor's work thread.
#[allow(clippy::large_enum_variant)]
#[derive(Debug)]
enum BatchMessage {
    /// This is ONLY sent when the number of logs records in the data channel has reached `max_export_batch_size`.
    ExportLog(Arc<AtomicBool>),
    /// ForceFlush flushes the current buffer to the exporter.
    ForceFlush(mpsc::SyncSender<ExportResult>),
    /// Shut down the worker thread, push all logs in buffer to the exporter.
    Shutdown(mpsc::SyncSender<ExportResult>),
    /// Set the resource for the exporter.
    SetResource(Arc<Resource>),
}

type LogsData = Box<(LogRecord, InstrumentationScope)>;

/// The `BatchLogProcessor` collects finished logs in a buffer and exports them
/// in batches to the configured `LogExporter`. This processor is ideal for
/// high-throughput environments, as it minimizes the overhead of exporting logs
/// individually. It uses a **dedicated background thread** to manage and export logs
/// asynchronously, ensuring that the application's main execution flow is not blocked.
///
/// - This processor supports the following configurations:
///     - **Queue size**: Maximum number of log records that can be buffered.
///     - **Batch size**: Maximum number of log records to include in a single export.
///     - **Export timeout**: Maximum duration allowed for an export operation.
///     - **Scheduled delay**: Frequency at which the batch is exported.
///
/// When using this processor with the OTLP Exporter, the following exporter
/// features are supported:
/// - `grpc-tonic`: This requires `MeterProvider` to be created within a tokio
///   runtime.
/// - `reqwest-blocking-client`: Works with a regular `main` or `tokio::main`.
///
/// In other words, other clients like `reqwest` and `hyper` are not supported.
///
/// ### Using a BatchLogProcessor:
///
/// ```rust
/// use opentelemetry_sdk::logs::{BatchLogProcessor, BatchConfigBuilder, LoggerProvider};
/// use opentelemetry::global;
/// use std::time::Duration;
/// use opentelemetry_sdk::testing::logs::InMemoryLogExporter;
///
/// let exporter = InMemoryLogExporter::default(); // Replace with an actual exporter
/// let processor = BatchLogProcessor::builder(exporter)
///     .with_batch_config(
///         BatchConfigBuilder::default()
///             .with_max_queue_size(2048)
///             .with_max_export_batch_size(512)
///             .with_scheduled_delay(Duration::from_secs(5))
///             .with_max_export_timeout(Duration::from_secs(30))
///             .build(),
///     )
///     .build();
///
/// let provider = LoggerProvider::builder()
///     .with_log_processor(processor)
///     .build();
///
pub struct BatchLogProcessor {
    logs_sender: SyncSender<LogsData>, // Data channel to store log records and instrumentation scopes
    message_sender: SyncSender<BatchMessage>, // Control channel to store control messages for the worker thread
    handle: Mutex<Option<thread::JoinHandle<()>>>,
    forceflush_timeout: Duration,
    shutdown_timeout: Duration,
    is_shutdown: AtomicBool,
    export_log_message_sent: Arc<AtomicBool>,
    current_batch_size: Arc<AtomicUsize>,
    max_export_batch_size: usize,

    // Track dropped logs - we'll log this at shutdown
    dropped_logs_count: AtomicUsize,

    // Track the maximum queue size that was configured for this processor
    max_queue_size: usize,
}

impl Debug for BatchLogProcessor {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        f.debug_struct("BatchLogProcessor")
            .field("message_sender", &self.message_sender)
            .finish()
    }
}

impl LogProcessor for BatchLogProcessor {
    fn emit(&self, record: &mut LogRecord, instrumentation: &InstrumentationScope) {
        // noop after shutdown
        if self.is_shutdown.load(std::sync::atomic::Ordering::Relaxed) {
            otel_warn!(
                name: "BatchLogProcessor.Emit.ProcessorShutdown",
                message = "BatchLogProcessor has been shutdown. No further logs will be emitted."
            );
            return;
        }

        let result = self
            .logs_sender
            .try_send(Box::new((record.clone(), instrumentation.clone())));

        if result.is_err() {
            // Increment dropped logs count. The first time we have to drop a log,
            // emit a warning.
            if self.dropped_logs_count.fetch_add(1, Ordering::Relaxed) == 0 {
                otel_warn!(name: "BatchLogProcessor.LogDroppingStarted",
                    message = "BatchLogProcessor dropped a LogRecord due to queue full/internal errors. No further log will be emitted for further drops until Shutdown. During Shutdown time, a log will be emitted with exact count of total logs dropped.");
            }
            return;
        }

        // At this point, sending the log record to the data channel was successful.
        // Increment the current batch size and check if it has reached the max export batch size.
        if self.current_batch_size.fetch_add(1, Ordering::Relaxed) + 1 >= self.max_export_batch_size
        {
            // Check if the a control message for exporting logs is already sent to the worker thread.
            // If not, send a control message to export logs.
            // `export_log_message_sent` is set to false ONLY when the worker thread has processed the control message.

            if !self.export_log_message_sent.load(Ordering::Relaxed) {
                // This is a cost-efficient check as atomic load operations do not require exclusive access to cache line.
                // Perform atomic swap to `export_log_message_sent` ONLY when the atomic load operation above returns false.
                // Atomic swap/compare_exchange operations require exclusive access to cache line on most processor architectures.
                // We could have used compare_exchange as well here, but it's more verbose than swap.
                if !self.export_log_message_sent.swap(true, Ordering::Relaxed) {
                    match self.message_sender.try_send(BatchMessage::ExportLog(
                        self.export_log_message_sent.clone(),
                    )) {
                        Ok(_) => {
                            // Control message sent successfully.
                        }
                        Err(_err) => {
                            // TODO: Log error
                            // If the control message could not be sent, reset the `export_log_message_sent` flag.
                            self.export_log_message_sent.store(false, Ordering::Relaxed);
                        }
                    }
                }
            }
        }
    }

    fn force_flush(&self) -> LogResult<()> {
        if self.is_shutdown.load(std::sync::atomic::Ordering::Relaxed) {
            return LogResult::Err(LogError::Other(
                "BatchLogProcessor is already shutdown".into(),
            ));
        }
        let (sender, receiver) = mpsc::sync_channel(1);
        self.message_sender
            .try_send(BatchMessage::ForceFlush(sender))
            .map_err(|err| LogError::Other(err.into()))?;

        receiver
            .recv_timeout(self.forceflush_timeout)
            .map_err(|err| {
                if err == RecvTimeoutError::Timeout {
                    LogError::ExportTimedOut(self.forceflush_timeout)
                } else {
                    LogError::Other(err.into())
                }
            })?
    }

    fn shutdown(&self) -> LogResult<()> {
        // Set is_shutdown to true
        self.is_shutdown
            .store(true, std::sync::atomic::Ordering::Relaxed);

        let dropped_logs = self.dropped_logs_count.load(Ordering::Relaxed);
        let max_queue_size = self.max_queue_size;
        if dropped_logs > 0 {
            otel_warn!(
                name: "BatchLogProcessor.LogsDropped",
                dropped_logs_count = dropped_logs,
                max_queue_size = max_queue_size,
                message = "Logs were dropped due to a queue being full or other error. The count represents the total count of log records dropped in the lifetime of this BatchLogProcessor. Consider increasing the queue size and/or decrease delay between intervals."
            );
        }

        let (sender, receiver) = mpsc::sync_channel(1);
        self.message_sender
            .try_send(BatchMessage::Shutdown(sender))
            .map_err(|err| LogError::Other(err.into()))?;

        receiver
            .recv_timeout(self.shutdown_timeout)
            .map(|_| {
                // join the background thread after receiving back the shutdown signal
                if let Some(handle) = self.handle.lock().unwrap().take() {
                    handle.join().unwrap();
                }
                LogResult::Ok(())
            })
            .map_err(|err| match err {
                RecvTimeoutError::Timeout => {
                    otel_error!(
                        name: "BatchLogProcessor.Shutdown.Timeout",
                        message = "BatchLogProcessor shutdown timing out."
                    );
                    LogError::ExportTimedOut(self.shutdown_timeout)
                }
                _ => {
                    otel_error!(
                        name: "BatchLogProcessor.Shutdown.Error",
                        error = format!("{}", err)
                    );
                    LogError::Other(err.into())
                }
            })?
    }

    fn set_resource(&self, resource: &Resource) {
        let resource = Arc::new(resource.clone());
        let _ = self
            .message_sender
            .try_send(BatchMessage::SetResource(resource));
    }
}

impl BatchLogProcessor {
    pub(crate) fn new<E>(mut exporter: E, config: BatchConfig) -> Self
    where
        E: LogExporter + Send + Sync + 'static,
    {
        let (logs_sender, logs_receiver) = mpsc::sync_channel::<LogsData>(config.max_queue_size);
        let (message_sender, message_receiver) = mpsc::sync_channel::<BatchMessage>(64); // Is this a reasonable bound?
        let max_queue_size = config.max_queue_size;
        let max_export_batch_size = config.max_export_batch_size;
        let current_batch_size = Arc::new(AtomicUsize::new(0));
        let current_batch_size_for_thread = current_batch_size.clone();

        let handle = thread::Builder::new()
            .name("OpenTelemetry.Logs.BatchProcessor".to_string())
            .spawn(move || {
                otel_info!(
                    name: "BatchLogProcessor.ThreadStarted",
                    interval_in_millisecs = config.scheduled_delay.as_millis(),
                    max_export_batch_size = config.max_export_batch_size,
                    max_queue_size = max_queue_size,
                );
                let mut last_export_time = Instant::now();
                let mut logs = Vec::with_capacity(config.max_export_batch_size);
                let current_batch_size = current_batch_size_for_thread;

                // This method gets upto `max_export_batch_size` amount of logs from the channel and exports them.
                // It returns the result of the export operation.
                // It expects the logs vec to be empty when it's called.
                #[inline]
                fn get_logs_and_export<E>(
                    logs_receiver: &mpsc::Receiver<LogsData>,
                    exporter: &E,
                    logs: &mut Vec<LogsData>,
                    last_export_time: &mut Instant,
                    current_batch_size: &AtomicUsize,
                    config: &BatchConfig,
                ) -> ExportResult
                where
                    E: LogExporter + Send + Sync + 'static,
                {
                    let target = current_batch_size.load(Ordering::Relaxed); // `target` is used to determine the stopping criteria for exporting logs.
                    let mut result = LogResult::Ok(());
                    let mut total_exported_logs: usize = 0;

                    while target > 0 && total_exported_logs < target {
                        // Get upto `max_export_batch_size` amount of logs log records from the channel and push them to the logs vec
                        while let Ok(log) = logs_receiver.try_recv() {
                            logs.push(log);
                            if logs.len() == config.max_export_batch_size {
                                break;
                            }
                        }

                        let count_of_logs = logs.len(); // Count of logs that will be exported
                        total_exported_logs += count_of_logs;

                        result = export_with_timeout_sync(
                            config.max_export_timeout,
                            exporter,
                            logs,
                            last_export_time,
                        ); // This method clears the logs vec after exporting

                        current_batch_size.fetch_sub(count_of_logs, Ordering::Relaxed);
                    }
                    result
                }

                loop {
                    let remaining_time = config
                        .scheduled_delay
                        .checked_sub(last_export_time.elapsed())
                        .unwrap_or(config.scheduled_delay);

                    match message_receiver.recv_timeout(remaining_time) {
                        Ok(BatchMessage::ExportLog(export_log_message_sent)) => {
                            // Reset the export log message sent flag now it has has been processed.
                            export_log_message_sent.store(false, Ordering::Relaxed);

                            otel_debug!(
                                name: "BatchLogProcessor.ExportingDueToBatchSize",
                            );

                            let _ = get_logs_and_export(
                                &logs_receiver,
                                &exporter,
                                &mut logs,
                                &mut last_export_time,
                                &current_batch_size,
                                &config,
                            );
                        }
                        Ok(BatchMessage::ForceFlush(sender)) => {
                            otel_debug!(name: "BatchLogProcessor.ExportingDueToForceFlush");
                            let result = get_logs_and_export(
                                &logs_receiver,
                                &exporter,
                                &mut logs,
                                &mut last_export_time,
                                &current_batch_size,
                                &config,
                            );
                            let _ = sender.send(result);
                        }
                        Ok(BatchMessage::Shutdown(sender)) => {
                            otel_debug!(name: "BatchLogProcessor.ExportingDueToShutdown");
                            let result = get_logs_and_export(
                                &logs_receiver,
                                &exporter,
                                &mut logs,
                                &mut last_export_time,
                                &current_batch_size,
                                &config,
                            );
                            let _ = sender.send(result);

                            otel_debug!(
                                name: "BatchLogProcessor.ThreadExiting",
                                reason = "ShutdownRequested"
                            );
                            //
                            // break out the loop and return from the current background thread.
                            //
                            break;
                        }
                        Ok(BatchMessage::SetResource(resource)) => {
                            exporter.set_resource(&resource);
                        }
                        Err(RecvTimeoutError::Timeout) => {
                            otel_debug!(
                                name: "BatchLogProcessor.ExportingDueToTimer",
                            );

                            let _ = get_logs_and_export(
                                &logs_receiver,
                                &exporter,
                                &mut logs,
                                &mut last_export_time,
                                &current_batch_size,
                                &config,
                            );
                        }
                        Err(RecvTimeoutError::Disconnected) => {
                            // Channel disconnected, only thing to do is break
                            // out (i.e exit the thread)
                            otel_debug!(
                                name: "BatchLogProcessor.ThreadExiting",
                                reason = "MessageSenderDisconnected"
                            );
                            break;
                        }
                    }
                }
                otel_info!(
                    name: "BatchLogProcessor.ThreadStopped"
                );
            })
            .expect("Thread spawn failed."); //TODO: Handle thread spawn failure

        // Return batch processor with link to worker
        BatchLogProcessor {
            logs_sender,
            message_sender,
            handle: Mutex::new(Some(handle)),
            forceflush_timeout: Duration::from_secs(5), // TODO: make this configurable
            shutdown_timeout: Duration::from_secs(5),   // TODO: make this configurable
            is_shutdown: AtomicBool::new(false),
            dropped_logs_count: AtomicUsize::new(0),
            max_queue_size,
            export_log_message_sent: Arc::new(AtomicBool::new(false)),
            current_batch_size,
            max_export_batch_size,
        }
    }

    /// Create a new batch processor builder
    pub fn builder<E>(exporter: E) -> BatchLogProcessorBuilder<E>
    where
        E: LogExporter,
    {
        BatchLogProcessorBuilder {
            exporter,
            config: Default::default(),
        }
    }
}

#[allow(clippy::vec_box)]
fn export_with_timeout_sync<E>(
    _: Duration, // TODO, enforcing timeout in exporter.
    exporter: &E,
    batch: &mut Vec<Box<(LogRecord, InstrumentationScope)>>,
    last_export_time: &mut Instant,
) -> ExportResult
where
    E: LogExporter + ?Sized,
{
    *last_export_time = Instant::now();

    if batch.is_empty() {
        return LogResult::Ok(());
    }

    let export = exporter.export(LogBatch::new_with_owned_data(batch.as_slice()));
    let export_result = futures_executor::block_on(export);

    // Clear the batch vec after exporting
    batch.clear();

    match export_result {
        Ok(_) => LogResult::Ok(()),
        Err(err) => {
            otel_error!(
                name: "BatchLogProcessor.ExportError",
                error = format!("{}", err)
            );
            LogResult::Err(err)
        }
    }
}

///
/// A builder for creating [`BatchLogProcessor`] instances.
///
#[derive(Debug)]
pub struct BatchLogProcessorBuilder<E> {
    exporter: E,
    config: BatchConfig,
}

impl<E> BatchLogProcessorBuilder<E>
where
    E: LogExporter + 'static,
{
    /// Set the BatchConfig for [`BatchLogProcessorBuilder`]
    pub fn with_batch_config(self, config: BatchConfig) -> Self {
        BatchLogProcessorBuilder { config, ..self }
    }

    /// Build a batch processor
    pub fn build(self) -> BatchLogProcessor {
        BatchLogProcessor::new(self.exporter, self.config)
    }
}

/// Batch log processor configuration.
/// Use [`BatchConfigBuilder`] to configure your own instance of [`BatchConfig`].
#[derive(Debug)]
#[allow(dead_code)]
pub struct BatchConfig {
    /// The maximum queue size to buffer logs for delayed processing. If the
    /// queue gets full it drops the logs. The default value of is 2048.
    pub(crate) max_queue_size: usize,

    /// The delay interval in milliseconds between two consecutive processing
    /// of batches. The default value is 1 second.
    pub(crate) scheduled_delay: Duration,

    /// The maximum number of logs to process in a single batch. If there are
    /// more than one batch worth of logs then it processes multiple batches
    /// of logs one batch after the other without any delay. The default value
    /// is 512.
    pub(crate) max_export_batch_size: usize,

    /// The maximum duration to export a batch of data.
    pub(crate) max_export_timeout: Duration,
}

impl Default for BatchConfig {
    fn default() -> Self {
        BatchConfigBuilder::default().build()
    }
}

/// A builder for creating [`BatchConfig`] instances.
#[derive(Debug)]
pub struct BatchConfigBuilder {
    max_queue_size: usize,
    scheduled_delay: Duration,
    max_export_batch_size: usize,
    max_export_timeout: Duration,
}

impl Default for BatchConfigBuilder {
    /// Create a new [`BatchConfigBuilder`] initialized with default batch config values as per the specs.
    /// The values are overridden by environment variables if set.
    /// The supported environment variables are:
    /// * `OTEL_BLRP_MAX_QUEUE_SIZE`
    /// * `OTEL_BLRP_SCHEDULE_DELAY`
    /// * `OTEL_BLRP_MAX_EXPORT_BATCH_SIZE`
    /// * `OTEL_BLRP_EXPORT_TIMEOUT`
    fn default() -> Self {
        BatchConfigBuilder {
            max_queue_size: OTEL_BLRP_MAX_QUEUE_SIZE_DEFAULT,
            scheduled_delay: Duration::from_millis(OTEL_BLRP_SCHEDULE_DELAY_DEFAULT),
            max_export_batch_size: OTEL_BLRP_MAX_EXPORT_BATCH_SIZE_DEFAULT,
            max_export_timeout: Duration::from_millis(OTEL_BLRP_EXPORT_TIMEOUT_DEFAULT),
        }
        .init_from_env_vars()
    }
}

impl BatchConfigBuilder {
    /// Set max_queue_size for [`BatchConfigBuilder`].
    /// It's the maximum queue size to buffer logs for delayed processing.
    /// If the queue gets full it will drop the logs.
    /// The default value of is 2048.
    pub fn with_max_queue_size(mut self, max_queue_size: usize) -> Self {
        self.max_queue_size = max_queue_size;
        self
    }

    /// Set scheduled_delay for [`BatchConfigBuilder`].
    /// It's the delay interval in milliseconds between two consecutive processing of batches.
    /// The default value is 1000 milliseconds.
    pub fn with_scheduled_delay(mut self, scheduled_delay: Duration) -> Self {
        self.scheduled_delay = scheduled_delay;
        self
    }

    /// Set max_export_timeout for [`BatchConfigBuilder`].
    /// It's the maximum duration to export a batch of data.
    /// The default value is 30000 milliseconds.
    pub fn with_max_export_timeout(mut self, max_export_timeout: Duration) -> Self {
        self.max_export_timeout = max_export_timeout;
        self
    }

    /// Set max_export_batch_size for [`BatchConfigBuilder`].
    /// It's the maximum number of logs to process in a single batch. If there are
    /// more than one batch worth of logs then it processes multiple batches
    /// of logs one batch after the other without any delay.
    /// The default value is 512.
    pub fn with_max_export_batch_size(mut self, max_export_batch_size: usize) -> Self {
        self.max_export_batch_size = max_export_batch_size;
        self
    }

    /// Builds a `BatchConfig` enforcing the following invariants:
    /// * `max_export_batch_size` must be less than or equal to `max_queue_size`.
    pub fn build(self) -> BatchConfig {
        // max export batch size must be less or equal to max queue size.
        // we set max export batch size to max queue size if it's larger than max queue size.
        let max_export_batch_size = min(self.max_export_batch_size, self.max_queue_size);

        BatchConfig {
            max_queue_size: self.max_queue_size,
            scheduled_delay: self.scheduled_delay,
            max_export_timeout: self.max_export_timeout,
            max_export_batch_size,
        }
    }

    fn init_from_env_vars(mut self) -> Self {
        if let Some(max_queue_size) = env::var(OTEL_BLRP_MAX_QUEUE_SIZE)
            .ok()
            .and_then(|queue_size| usize::from_str(&queue_size).ok())
        {
            self.max_queue_size = max_queue_size;
        }

        if let Some(max_export_batch_size) = env::var(OTEL_BLRP_MAX_EXPORT_BATCH_SIZE)
            .ok()
            .and_then(|batch_size| usize::from_str(&batch_size).ok())
        {
            self.max_export_batch_size = max_export_batch_size;
        }

        if let Some(scheduled_delay) = env::var(OTEL_BLRP_SCHEDULE_DELAY)
            .ok()
            .and_then(|delay| u64::from_str(&delay).ok())
        {
            self.scheduled_delay = Duration::from_millis(scheduled_delay);
        }

        if let Some(max_export_timeout) = env::var(OTEL_BLRP_EXPORT_TIMEOUT)
            .ok()
            .and_then(|s| u64::from_str(&s).ok())
        {
            self.max_export_timeout = Duration::from_millis(max_export_timeout);
        }

        self
    }
}

#[cfg(all(test, feature = "testing", feature = "logs"))]
mod tests {
    use super::{
        BatchLogProcessor, OTEL_BLRP_EXPORT_TIMEOUT, OTEL_BLRP_MAX_EXPORT_BATCH_SIZE,
        OTEL_BLRP_MAX_QUEUE_SIZE, OTEL_BLRP_SCHEDULE_DELAY,
    };
    use crate::export::logs::{LogBatch, LogExporter};
    use crate::logs::LogRecord;
    use crate::logs::LogResult;
    use crate::testing::logs::InMemoryLogExporterBuilder;
    use crate::{
        logs::{
            log_processor::{
                OTEL_BLRP_EXPORT_TIMEOUT_DEFAULT, OTEL_BLRP_MAX_EXPORT_BATCH_SIZE_DEFAULT,
                OTEL_BLRP_MAX_QUEUE_SIZE_DEFAULT, OTEL_BLRP_SCHEDULE_DELAY_DEFAULT,
            },
            BatchConfig, BatchConfigBuilder, LogProcessor, LoggerProvider, SimpleLogProcessor,
        },
        testing::logs::InMemoryLogExporter,
        Resource,
    };
    use opentelemetry::logs::AnyValue;
    use opentelemetry::logs::LogRecord as _;
    use opentelemetry::logs::{Logger, LoggerProvider as _};
    use opentelemetry::KeyValue;
    use opentelemetry::{InstrumentationScope, Key};
    use std::sync::atomic::{AtomicUsize, Ordering};
    use std::sync::{Arc, Mutex};
    use std::time::Duration;

    #[derive(Debug, Clone)]
    struct MockLogExporter {
        resource: Arc<Mutex<Option<Resource>>>,
    }

    impl LogExporter for MockLogExporter {
        #[allow(clippy::manual_async_fn)]
        fn export(
            &self,
            _batch: LogBatch<'_>,
        ) -> impl std::future::Future<Output = LogResult<()>> + Send {
            async { Ok(()) }
        }

        fn shutdown(&mut self) {}

        fn set_resource(&mut self, resource: &Resource) {
            self.resource
                .lock()
                .map(|mut res_opt| {
                    res_opt.replace(resource.clone());
                })
                .expect("mock log exporter shouldn't error when setting resource");
        }
    }

    // Implementation specific to the MockLogExporter, not part of the LogExporter trait
    impl MockLogExporter {
        fn get_resource(&self) -> Option<Resource> {
            (*self.resource).lock().unwrap().clone()
        }
    }

    #[test]
    fn test_default_const_values() {
        assert_eq!(OTEL_BLRP_SCHEDULE_DELAY, "OTEL_BLRP_SCHEDULE_DELAY");
        assert_eq!(OTEL_BLRP_SCHEDULE_DELAY_DEFAULT, 1_000);
        assert_eq!(OTEL_BLRP_EXPORT_TIMEOUT, "OTEL_BLRP_EXPORT_TIMEOUT");
        assert_eq!(OTEL_BLRP_EXPORT_TIMEOUT_DEFAULT, 30_000);
        assert_eq!(OTEL_BLRP_MAX_QUEUE_SIZE, "OTEL_BLRP_MAX_QUEUE_SIZE");
        assert_eq!(OTEL_BLRP_MAX_QUEUE_SIZE_DEFAULT, 2_048);
        assert_eq!(
            OTEL_BLRP_MAX_EXPORT_BATCH_SIZE,
            "OTEL_BLRP_MAX_EXPORT_BATCH_SIZE"
        );
        assert_eq!(OTEL_BLRP_MAX_EXPORT_BATCH_SIZE_DEFAULT, 512);
    }

    #[test]
    fn test_default_batch_config_adheres_to_specification() {
        // The following environment variables are expected to be unset so that their default values are used.
        let env_vars = vec![
            OTEL_BLRP_SCHEDULE_DELAY,
            OTEL_BLRP_EXPORT_TIMEOUT,
            OTEL_BLRP_MAX_QUEUE_SIZE,
            OTEL_BLRP_MAX_EXPORT_BATCH_SIZE,
        ];

        let config = temp_env::with_vars_unset(env_vars, BatchConfig::default);

        assert_eq!(
            config.scheduled_delay,
            Duration::from_millis(OTEL_BLRP_SCHEDULE_DELAY_DEFAULT)
        );
        assert_eq!(
            config.max_export_timeout,
            Duration::from_millis(OTEL_BLRP_EXPORT_TIMEOUT_DEFAULT)
        );
        assert_eq!(config.max_queue_size, OTEL_BLRP_MAX_QUEUE_SIZE_DEFAULT);
        assert_eq!(
            config.max_export_batch_size,
            OTEL_BLRP_MAX_EXPORT_BATCH_SIZE_DEFAULT
        );
    }

    #[test]
    fn test_batch_config_configurable_by_env_vars() {
        let env_vars = vec![
            (OTEL_BLRP_SCHEDULE_DELAY, Some("2000")),
            (OTEL_BLRP_EXPORT_TIMEOUT, Some("60000")),
            (OTEL_BLRP_MAX_QUEUE_SIZE, Some("4096")),
            (OTEL_BLRP_MAX_EXPORT_BATCH_SIZE, Some("1024")),
        ];

        let config = temp_env::with_vars(env_vars, BatchConfig::default);

        assert_eq!(config.scheduled_delay, Duration::from_millis(2000));
        assert_eq!(config.max_export_timeout, Duration::from_millis(60000));
        assert_eq!(config.max_queue_size, 4096);
        assert_eq!(config.max_export_batch_size, 1024);
    }

    #[test]
    fn test_batch_config_max_export_batch_size_validation() {
        let env_vars = vec![
            (OTEL_BLRP_MAX_QUEUE_SIZE, Some("256")),
            (OTEL_BLRP_MAX_EXPORT_BATCH_SIZE, Some("1024")),
        ];

        let config = temp_env::with_vars(env_vars, BatchConfig::default);

        assert_eq!(config.max_queue_size, 256);
        assert_eq!(config.max_export_batch_size, 256);
        assert_eq!(
            config.scheduled_delay,
            Duration::from_millis(OTEL_BLRP_SCHEDULE_DELAY_DEFAULT)
        );
        assert_eq!(
            config.max_export_timeout,
            Duration::from_millis(OTEL_BLRP_EXPORT_TIMEOUT_DEFAULT)
        );
    }

    #[test]
    fn test_batch_config_with_fields() {
        let batch = BatchConfigBuilder::default()
            .with_max_export_batch_size(1)
            .with_scheduled_delay(Duration::from_millis(2))
            .with_max_export_timeout(Duration::from_millis(3))
            .with_max_queue_size(4)
            .build();

        assert_eq!(batch.max_export_batch_size, 1);
        assert_eq!(batch.scheduled_delay, Duration::from_millis(2));
        assert_eq!(batch.max_export_timeout, Duration::from_millis(3));
        assert_eq!(batch.max_queue_size, 4);
    }

    #[test]
    fn test_build_batch_log_processor_builder() {
        let mut env_vars = vec![
            (OTEL_BLRP_MAX_EXPORT_BATCH_SIZE, Some("500")),
            (OTEL_BLRP_SCHEDULE_DELAY, Some("I am not number")),
            (OTEL_BLRP_EXPORT_TIMEOUT, Some("2046")),
        ];
        temp_env::with_vars(env_vars.clone(), || {
            let builder = BatchLogProcessor::builder(InMemoryLogExporter::default());

            assert_eq!(builder.config.max_export_batch_size, 500);
            assert_eq!(
                builder.config.scheduled_delay,
                Duration::from_millis(OTEL_BLRP_SCHEDULE_DELAY_DEFAULT)
            );
            assert_eq!(
                builder.config.max_queue_size,
                OTEL_BLRP_MAX_QUEUE_SIZE_DEFAULT
            );
            assert_eq!(
                builder.config.max_export_timeout,
                Duration::from_millis(2046)
            );
        });

        env_vars.push((OTEL_BLRP_MAX_QUEUE_SIZE, Some("120")));

        temp_env::with_vars(env_vars, || {
            let builder = BatchLogProcessor::builder(InMemoryLogExporter::default());
            assert_eq!(builder.config.max_export_batch_size, 120);
            assert_eq!(builder.config.max_queue_size, 120);
        });
    }

    #[test]
    fn test_build_batch_log_processor_builder_with_custom_config() {
        let expected = BatchConfigBuilder::default()
            .with_max_export_batch_size(1)
            .with_scheduled_delay(Duration::from_millis(2))
            .with_max_export_timeout(Duration::from_millis(3))
            .with_max_queue_size(4)
            .build();

        let builder =
            BatchLogProcessor::builder(InMemoryLogExporter::default()).with_batch_config(expected);

        let actual = &builder.config;
        assert_eq!(actual.max_export_batch_size, 1);
        assert_eq!(actual.scheduled_delay, Duration::from_millis(2));
        assert_eq!(actual.max_export_timeout, Duration::from_millis(3));
        assert_eq!(actual.max_queue_size, 4);
    }

    #[test]
    fn test_set_resource_simple_processor() {
        let exporter = MockLogExporter {
            resource: Arc::new(Mutex::new(None)),
        };
        let processor = SimpleLogProcessor::new(exporter.clone());
        let _ = LoggerProvider::builder()
            .with_log_processor(processor)
            .with_resource(
                Resource::builder_empty()
                    .with_attributes([
                        KeyValue::new("k1", "v1"),
                        KeyValue::new("k2", "v3"),
                        KeyValue::new("k3", "v3"),
                        KeyValue::new("k4", "v4"),
                        KeyValue::new("k5", "v5"),
                    ])
                    .build(),
            )
            .build();
        assert_eq!(exporter.get_resource().unwrap().into_iter().count(), 5);
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
    async fn test_set_resource_batch_processor() {
        let exporter = MockLogExporter {
            resource: Arc::new(Mutex::new(None)),
        };
        let processor = BatchLogProcessor::new(exporter.clone(), BatchConfig::default());
        let provider = LoggerProvider::builder()
            .with_log_processor(processor)
            .with_resource(
                Resource::builder_empty()
                    .with_attributes([
                        KeyValue::new("k1", "v1"),
                        KeyValue::new("k2", "v3"),
                        KeyValue::new("k3", "v3"),
                        KeyValue::new("k4", "v4"),
                        KeyValue::new("k5", "v5"),
                    ])
                    .build(),
            )
            .build();

        // wait for the batch processor to process the resource.
        tokio::time::sleep(Duration::from_millis(100)).await;

        assert_eq!(exporter.get_resource().unwrap().into_iter().count(), 5);
        let _ = provider.shutdown();
    }

    #[tokio::test(flavor = "multi_thread")]
    async fn test_batch_shutdown() {
        // assert we will receive an error
        // setup
        let exporter = InMemoryLogExporterBuilder::default()
            .keep_records_on_shutdown()
            .build();
        let processor = BatchLogProcessor::new(exporter.clone(), BatchConfig::default());

        let mut record = LogRecord::default();
        let instrumentation = InstrumentationScope::default();

        processor.emit(&mut record, &instrumentation);
        processor.force_flush().unwrap();
        processor.shutdown().unwrap();
        // todo: expect to see errors here. How should we assert this?
        processor.emit(&mut record, &instrumentation);
        assert_eq!(1, exporter.get_emitted_logs().unwrap().len())
    }

    #[test]
    fn test_simple_shutdown() {
        let exporter = InMemoryLogExporterBuilder::default()
            .keep_records_on_shutdown()
            .build();
        let processor = SimpleLogProcessor::new(exporter.clone());

        let mut record: LogRecord = Default::default();
        let instrumentation: InstrumentationScope = Default::default();

        processor.emit(&mut record, &instrumentation);

        processor.shutdown().unwrap();

        let is_shutdown = processor
            .is_shutdown
            .load(std::sync::atomic::Ordering::Relaxed);
        assert!(is_shutdown);

        processor.emit(&mut record, &instrumentation);

        assert_eq!(1, exporter.get_emitted_logs().unwrap().len())
    }

    #[tokio::test(flavor = "current_thread")]
    async fn test_batch_log_processor_shutdown_under_async_runtime_current_flavor_multi_thread() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = BatchLogProcessor::new(exporter.clone(), BatchConfig::default());

        processor.shutdown().unwrap();
    }

    #[tokio::test(flavor = "current_thread")]
    async fn test_batch_log_processor_shutdown_with_async_runtime_current_flavor_current_thread() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = BatchLogProcessor::new(exporter.clone(), BatchConfig::default());
        processor.shutdown().unwrap();
    }

    #[tokio::test(flavor = "multi_thread")]
    async fn test_batch_log_processor_shutdown_with_async_runtime_multi_flavor_multi_thread() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = BatchLogProcessor::new(exporter.clone(), BatchConfig::default());
        processor.shutdown().unwrap();
    }

    #[tokio::test(flavor = "multi_thread")]
    async fn test_batch_log_processor_shutdown_with_async_runtime_multi_flavor_current_thread() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = BatchLogProcessor::new(exporter.clone(), BatchConfig::default());
        processor.shutdown().unwrap();
    }

    #[derive(Debug)]
    struct FirstProcessor {
        pub(crate) logs: Arc<Mutex<Vec<(LogRecord, InstrumentationScope)>>>,
    }

    impl LogProcessor for FirstProcessor {
        fn emit(&self, record: &mut LogRecord, instrumentation: &InstrumentationScope) {
            // add attribute
            record.add_attribute(
                Key::from_static_str("processed_by"),
                AnyValue::String("FirstProcessor".into()),
            );
            // update body
            record.body = Some("Updated by FirstProcessor".into());

            self.logs
                .lock()
                .unwrap()
                .push((record.clone(), instrumentation.clone())); //clone as the LogProcessor is storing the data.
        }

        fn force_flush(&self) -> LogResult<()> {
            Ok(())
        }

        fn shutdown(&self) -> LogResult<()> {
            Ok(())
        }
    }

    #[derive(Debug)]
    struct SecondProcessor {
        pub(crate) logs: Arc<Mutex<Vec<(LogRecord, InstrumentationScope)>>>,
    }

    impl LogProcessor for SecondProcessor {
        fn emit(&self, record: &mut LogRecord, instrumentation: &InstrumentationScope) {
            assert!(record.attributes_contains(
                &Key::from_static_str("processed_by"),
                &AnyValue::String("FirstProcessor".into())
            ));
            assert!(
                record.body.clone().unwrap()
                    == AnyValue::String("Updated by FirstProcessor".into())
            );
            self.logs
                .lock()
                .unwrap()
                .push((record.clone(), instrumentation.clone()));
        }

        fn force_flush(&self) -> LogResult<()> {
            Ok(())
        }

        fn shutdown(&self) -> LogResult<()> {
            Ok(())
        }
    }
    #[test]
    fn test_log_data_modification_by_multiple_processors() {
        let first_processor_logs = Arc::new(Mutex::new(Vec::new()));
        let second_processor_logs = Arc::new(Mutex::new(Vec::new()));

        let first_processor = FirstProcessor {
            logs: Arc::clone(&first_processor_logs),
        };
        let second_processor = SecondProcessor {
            logs: Arc::clone(&second_processor_logs),
        };

        let logger_provider = LoggerProvider::builder()
            .with_log_processor(first_processor)
            .with_log_processor(second_processor)
            .build();

        let logger = logger_provider.logger("test-logger");
        let mut log_record = logger.create_log_record();
        log_record.body = Some(AnyValue::String("Test log".into()));

        logger.emit(log_record);

        assert_eq!(first_processor_logs.lock().unwrap().len(), 1);
        assert_eq!(second_processor_logs.lock().unwrap().len(), 1);

        let first_log = &first_processor_logs.lock().unwrap()[0];
        let second_log = &second_processor_logs.lock().unwrap()[0];

        assert!(first_log.0.attributes_contains(
            &Key::from_static_str("processed_by"),
            &AnyValue::String("FirstProcessor".into())
        ));
        assert!(second_log.0.attributes_contains(
            &Key::from_static_str("processed_by"),
            &AnyValue::String("FirstProcessor".into())
        ));

        assert!(
            first_log.0.body.clone().unwrap()
                == AnyValue::String("Updated by FirstProcessor".into())
        );
        assert!(
            second_log.0.body.clone().unwrap()
                == AnyValue::String("Updated by FirstProcessor".into())
        );
    }

    #[test]
    fn test_simple_processor_sync_exporter_without_runtime() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = SimpleLogProcessor::new(exporter.clone());

        let mut record: LogRecord = Default::default();
        let instrumentation: InstrumentationScope = Default::default();

        processor.emit(&mut record, &instrumentation);

        assert_eq!(exporter.get_emitted_logs().unwrap().len(), 1);
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
    async fn test_simple_processor_sync_exporter_with_runtime() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = SimpleLogProcessor::new(exporter.clone());

        let mut record: LogRecord = Default::default();
        let instrumentation: InstrumentationScope = Default::default();

        processor.emit(&mut record, &instrumentation);

        assert_eq!(exporter.get_emitted_logs().unwrap().len(), 1);
    }

    #[tokio::test(flavor = "multi_thread")]
    async fn test_simple_processor_sync_exporter_with_multi_thread_runtime() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = Arc::new(SimpleLogProcessor::new(exporter.clone()));

        let mut handles = vec![];
        for _ in 0..10 {
            let processor_clone = Arc::clone(&processor);
            let handle = tokio::spawn(async move {
                let mut record: LogRecord = Default::default();
                let instrumentation: InstrumentationScope = Default::default();
                processor_clone.emit(&mut record, &instrumentation);
            });
            handles.push(handle);
        }

        for handle in handles {
            handle.await.unwrap();
        }

        assert_eq!(exporter.get_emitted_logs().unwrap().len(), 10);
    }

    #[tokio::test(flavor = "current_thread")]
    async fn test_simple_processor_sync_exporter_with_current_thread_runtime() {
        let exporter = InMemoryLogExporterBuilder::default().build();
        let processor = SimpleLogProcessor::new(exporter.clone());

        let mut record: LogRecord = Default::default();
        let instrumentation: InstrumentationScope = Default::default();

        processor.emit(&mut record, &instrumentation);

        assert_eq!(exporter.get_emitted_logs().unwrap().len(), 1);
    }

    #[derive(Debug, Clone)]
    struct LogExporterThatRequiresTokio {
        export_count: Arc<AtomicUsize>,
    }

    impl LogExporterThatRequiresTokio {
        /// Creates a new instance of `LogExporterThatRequiresTokio`.
        fn new() -> Self {
            LogExporterThatRequiresTokio {
                export_count: Arc::new(AtomicUsize::new(0)),
            }
        }

        /// Returns the number of logs stored in the exporter.
        fn len(&self) -> usize {
            self.export_count.load(Ordering::Acquire)
        }
    }

    impl LogExporter for LogExporterThatRequiresTokio {
        #[allow(clippy::manual_async_fn)]
        fn export(
            &self,
            batch: LogBatch<'_>,
        ) -> impl std::future::Future<Output = LogResult<()>> + Send {
            // Simulate minimal dependency on tokio by sleeping asynchronously for a short duration
            async move {
                tokio::time::sleep(Duration::from_millis(50)).await;

                for _ in batch.iter() {
                    self.export_count.fetch_add(1, Ordering::Acquire);
                }
                Ok(())
            }
        }
    }

    #[test]
    fn test_simple_processor_async_exporter_without_runtime() {
        // Use `catch_unwind` to catch the panic caused by missing Tokio runtime
        let result = std::panic::catch_unwind(|| {
            let exporter = LogExporterThatRequiresTokio::new();
            let processor = SimpleLogProcessor::new(exporter.clone());

            let mut record: LogRecord = Default::default();
            let instrumentation: InstrumentationScope = Default::default();

            // This will panic because an tokio async operation within exporter without a runtime.
            processor.emit(&mut record, &instrumentation);
        });

        // Verify that the panic occurred and check the panic message for the absence of a Tokio runtime
        assert!(
            result.is_err(),
            "The test should fail due to missing Tokio runtime, but it did not."
        );
        let panic_payload = result.unwrap_err();
        let panic_message = panic_payload
            .downcast_ref::<String>()
            .map(|s| s.as_str())
            .or_else(|| panic_payload.downcast_ref::<&str>().copied())
            .unwrap_or("No panic message");

        assert!(
            panic_message.contains("no reactor running")
                || panic_message.contains("must be called from the context of a Tokio 1.x runtime"),
            "Expected panic message about missing Tokio runtime, but got: {}",
            panic_message
        );
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 4)]
    #[ignore]
    // This test demonstrates a potential deadlock scenario in a multi-threaded Tokio runtime.
    // It spawns Tokio tasks equal to the number of runtime worker threads (4) to emit log events.
    // Each task attempts to acquire a mutex on the exporter in `SimpleLogProcessor::emit`.
    // Only one task obtains the lock, while the others are blocked, waiting for its release.
    //
    // The task holding the lock invokes the LogExporterThatRequiresTokio, which performs an
    // asynchronous operation (e.g., network I/O simulated by `tokio::sleep`). This operation
    // requires yielding control back to the Tokio runtime to make progress.
    //
    // However, all worker threads are occupied:
    // - One thread is executing the async exporter operation
    // - Three threads are blocked waiting for the mutex
    //
    // This leads to a deadlock as there are no available threads to drive the async operation
    // to completion, preventing the mutex from being released. Consequently, neither the blocked
    // tasks nor the exporter can proceed.
    async fn test_simple_processor_async_exporter_with_all_runtime_worker_threads_blocked() {
        let exporter = LogExporterThatRequiresTokio::new();
        let processor = Arc::new(SimpleLogProcessor::new(exporter.clone()));

        let concurrent_emit = 4; // number of worker threads

        let mut handles = vec![];
        // try send `concurrent_emit` events concurrently
        for _ in 0..concurrent_emit {
            let processor_clone = Arc::clone(&processor);
            let handle = tokio::spawn(async move {
                let mut record: LogRecord = Default::default();
                let instrumentation: InstrumentationScope = Default::default();
                processor_clone.emit(&mut record, &instrumentation);
            });
            handles.push(handle);
        }

        // below code won't get executed
        for handle in handles {
            handle.await.unwrap();
        }
        assert_eq!(exporter.len(), concurrent_emit);
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
    // This test uses a multi-threaded runtime setup with a single worker thread. Note that even
    // though only one worker thread is created, it is distinct from the main thread. The processor
    // emits a log event, and the exporter performs an async operation that requires the runtime.
    // The single worker thread handles this operation without deadlocking, as long as no other
    // tasks occupy the runtime.
    async fn test_simple_processor_async_exporter_with_runtime() {
        let exporter = LogExporterThatRequiresTokio::new();
        let processor = SimpleLogProcessor::new(exporter.clone());

        let mut record: LogRecord = Default::default();
        let instrumentation: InstrumentationScope = Default::default();

        processor.emit(&mut record, &instrumentation);

        assert_eq!(exporter.len(), 1);
    }

    #[tokio::test(flavor = "multi_thread")]
    // This test uses a multi-threaded runtime setup with the default number of worker threads.
    // The processor emits a log event, and the exporter, which requires the runtime for its async
    // operations, can access one of the available worker threads to complete its task. As there
    // are multiple threads, the exporter can proceed without blocking other tasks, ensuring the
    // test completes successfully.
    async fn test_simple_processor_async_exporter_with_multi_thread_runtime() {
        let exporter = LogExporterThatRequiresTokio::new();

        let processor = SimpleLogProcessor::new(exporter.clone());

        let mut record: LogRecord = Default::default();
        let instrumentation: InstrumentationScope = Default::default();

        processor.emit(&mut record, &instrumentation);

        assert_eq!(exporter.len(), 1);
    }

    #[tokio::test(flavor = "current_thread")]
    #[ignore]
    // This test uses a current-thread runtime, where all operations run on the main thread.
    // The processor emits a log event while the runtime is blocked using `futures::block_on`
    // to complete the export operation. The exporter, which performs an async operation and
    // requires the runtime, cannot progress because the main thread is already blocked.
    // This results in a deadlock, as the runtime cannot move forward.
    async fn test_simple_processor_async_exporter_with_current_thread_runtime() {
        let exporter = LogExporterThatRequiresTokio::new();

        let processor = SimpleLogProcessor::new(exporter.clone());

        let mut record: LogRecord = Default::default();
        let instrumentation: InstrumentationScope = Default::default();

        processor.emit(&mut record, &instrumentation);

        assert_eq!(exporter.len(), 1);
    }
}