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Sleep causes the thread or process to give up the remainder of its time slice and stay in the Not Runnable state for the specified duration. While there is generally a guarantee for the minimum time period, there is no strict guarantee that the thread will run immediately or soon, or even at all, once the specified time has passed.
The result is an indefinite postponement until the thread holding the lock can finish and release it. This is especially true on a single-processor system, where each waiting thread of the same priority is likely to waste its quantum (allocated time where a thread can run) spinning until the thread that holds the lock is finally finished.
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.
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.
In this way, there is a race condition between all the awakened threads. The first thread to run will win the race and find the condition satisfied, while the other threads will lose the race, and experience a spurious wakeup. [citation needed] The problem of spurious wakeup can be exacerbated on multiprocessor systems.
POSIX Threads is an API defined by the Institute of Electrical and Electronics Engineers (IEEE) standard POSIX.1c, Threads extensions (IEEE Std 1003.1c-1995). Implementations of the API are available on many Unix-like POSIX-conformant operating systems such as FreeBSD , NetBSD , OpenBSD , Linux , macOS , Android [ 1 ] , Solaris , Redox , and ...
List of C++ multi-threading libraries; Multithreading (computer architecture) ... Single instruction, multiple threads; Sleep (system call) Spurious wakeup; Stapl; T ...
As of C++ 20, semaphores are part of the language. Dijkstra's solution can easily be written in modern C++. The variable buffer_manipulation is a mutex. The semaphore feature of acquiring in one thread and releasing in another thread is not needed. The lock_guard() statement instead of a lock() and unlock() pair is C++ RAII. The lock_guard ...