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Busy-waiting itself can be made much less wasteful by using a delay function (e.g., sleep()) found in most operating systems. This puts a thread to sleep for a specified time, during which the thread will waste no CPU time. If the loop is checking something simple then it will spend most of its time asleep and will waste very little CPU time.
pthreads defines a set of C programming language types, functions and constants. It is implemented with a pthread.h header and a thread library. There are around 100 threads procedures, all prefixed pthread_ and they can be categorized into five groups: Thread management – creating, joining threads etc. Mutexes; Condition variables
The problem of spurious wakeup can be exacerbated on multiprocessor systems. When several threads are waiting on a single condition variable, the system may decide to wake all threads up when it's signaled.
The functions pthread_key_create and pthread_key_delete are used respectively to create and delete a key for thread-specific data. The type of the key is explicitly left opaque and is referred to as pthread_key_t. This key can be seen by all threads. In each thread, the key can be associated with thread-specific data via pthread_setspecific.
In the following piece of C code, the function is thread-safe, but not reentrant: # include <pthread.h> int increment_counter () { static int counter = 0 ; static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER ; // only allow one thread to increment at a time pthread_mutex_lock ( & mutex ); ++ counter ; // store value before any other ...
Those 2 thread both have thread_func(), as the thread function handler, which call pthread_barrier_wait (& barrier), while thread barrier expected 3 threads to call pthread_barrier_wait (THREAD_BARRIERS_NUMBER = 3) in order to be lifted. Change TOTAL_THREADS to 3 and the thread barrier is lifted:
As soon as the first thread in question is switched back to, its program counter will be at step 1c, and it will sleep and be unable to be woken up again, violating the invariant that it should have been on c's sleep-queue when it slept. Other race conditions depend on the ordering of steps 1a and 1b, and depend on where a context switch occurs.
In computer programming, a thread pool is a software design pattern for achieving concurrency of execution in a computer program. Often also called a replicated workers or worker-crew model , [ 1 ] a thread pool maintains multiple threads waiting for tasks to be allocated for concurrent execution by the supervising program.