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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
In the Pthreads API, memory local to a thread is designated with the term Thread-specific data. 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.
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One failure mode that could occur if these were not atomic is a missed wakeup, in which the thread could be on c's sleep-queue and have released the mutex, but a preemptive thread switch occurred before the thread went to sleep, and another thread called a signal operation (see below) on c moving the first thread back out of c's queue.
The threaded programming model provides developers with a useful abstraction of concurrent execution. Multithreading can also be applied to one process to enable parallel execution on a multiprocessing system. Multithreading libraries tend to provide a function call to create a new thread, which takes a function as a parameter.
In the C programming language, each thread has its own stack. However, a static variable is not kept on the stack; all threads share simultaneous access to it. If multiple threads overlap while running the same function, it is possible that a static variable might be changed by one thread while another is midway through checking it.
The barrier synchronization wait function for i th thread can be represented as: (Wbarrier)i=f ((Tbarrier)i, (Rthread)i) Where Wbarrier is the wait time for a thread, Tbarrier is the number of threads has arrived, and Rthread is the arrival rate of threads. [14]