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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.
Illustration of the dining philosophers problem. Each philosopher has a bowl of spaghetti and can reach two of the forks. In computer science, the dining philosophers problem is an example problem often used in concurrent algorithm design to illustrate synchronization issues and techniques for resolving them.
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.
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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.
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.
If the value stored at the address addr is val, puts the current thread to sleep. WAKE(addr, num) Wakes up num number of threads waiting on the address addr. For more advanced uses, there are a number of other operations, the most used being CMP_REQUEUE and WAKE_OP, which both function as more generic WAKE operations. [13]
std::this_thread::yield() in the language C++, introduced in C++11. The Yield method is provided in various object-oriented programming languages with multithreading support, such as C# and Java. [2] OOP languages generally provide class abstractions for thread objects. yield in Kotlin