[pull] master from netdata:master

[pull]

See Commits and Changes for more details.

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Created by pull[bot] (v2.0.0-alpha.1)

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Summary by Sourcery

Tests:

• Add new stress tests for various lock types, including mutex, rwlock, spinlock, rw spinlock, and waitq.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request introduces new stress tests for locks and reimplements the reader-writer spinlock.

Sequence diagram for the updated RW spinlock read locking process

sequenceDiagram
    participant T as Thread
    participant L as RW_SPINLOCK
    T->>L: rw_spinlock_read_lock()
    activate L
    L->>L: Increment counter atomically
    Note over L: Check if WRITER_BIT is set
    alt No writer holds the lock
        L-->>T: Return success
    else Writer holds the lock
        L->>L: Decrement counter
        L->>L: Exponential backoff sleep
        L->>L: Retry
    end
    deactivate L

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Sequence diagram for the updated RW spinlock write locking process

sequenceDiagram
    participant T as Thread
    participant L as RW_SPINLOCK
    T->>L: rw_spinlock_write_lock()
    activate L
    L->>L: Set WRITER_BIT atomically
    Note over L: Check previous value
    alt No readers or writers
        L->>L: Set writer thread ID
        L-->>T: Return success
    else Readers or writer present
        L->>L: Clear WRITER_BIT if readers present
        L->>L: Exponential backoff sleep
        L->>L: Retry
    end
    deactivate L

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Class diagram for the updated RW_SPINLOCK implementation

classDiagram
    class RW_SPINLOCK {
        +pid_t writer
        +uint32_t counter
        +rw_spinlock_init()
        +rw_spinlock_tryread_lock()
        +rw_spinlock_read_lock()
        +rw_spinlock_read_unlock()
        +rw_spinlock_trywrite_lock()
        +rw_spinlock_write_lock()
        +rw_spinlock_write_unlock()
    }
    note for RW_SPINLOCK "Changed counter from REFCOUNT to uint32_t
Added WRITER_BIT (1U << 31) for writer lock
Added READER_MASK (~WRITER_BIT) for reader count"

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Class diagram for the new benchmark structures

classDiagram
    class thread_context_t {
        +int thread_id
        +thread_type_t type
        +WAITQ_PRIORITY priority
        +lock_control_t* control
        +void* lock
        +ND_THREAD* thread
    }
    class lock_control_t {
        +uint64_t protected_counter
        +thread_stats_t stats[MAX_THREADS]
        +thread_control_t thread_controls[MAX_THREADS]
    }
    class thread_stats_t {
        +uint64_t locks
        +usec_t test_time
        +volatile int ready
    }
    class thread_control_t {
        +pthread_cond_t cond
        +pthread_mutex_t cond_mutex
        +uint64_t run_flag
    }
    thread_context_t --> lock_control_t
    lock_control_t --> thread_stats_t
    lock_control_t --> thread_control_t

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File-Level Changes

Change	Details	Files
Added stress tests for various lock types, including mutex, reader-writer lock, spinlock, reader-writer spinlock, and wait queue.	Introduced new unit test options lockstest and rwlockstest to the daemon's command-line arguments. Added benchmark.c, benchmark.h, benchmark-rw.c, and benchmark-rw.h to the build system. Included the new benchmark header files in libnetdata.h.	src/daemon/main.c CMakeLists.txt src/libnetdata/libnetdata.h src/libnetdata/locks/benchmark.c src/libnetdata/locks/benchmark.h src/libnetdata/locks/benchmark-rw.c src/libnetdata/locks/benchmark-rw.h
Reimplemented the reader-writer spinlock using atomic operations and a more efficient locking mechanism.	Changed the internal representation of the lock counter to use a 32-bit unsigned integer. Simplified the read and write lock acquisition and release logic using atomic fetch-and-or and fetch-and-and operations. Introduced exponential backoff with a maximum limit for read and write lock acquisition. Removed unnecessary checks and simplified the code in waitq.c.	src/libnetdata/locks/rw-spinlock.c src/libnetdata/locks/rw-spinlock.h src/libnetdata/locks/waitq.c

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