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An uninterruptible sleep state is a sleep state that will not handle a signal right away. It will wake only as a result of a waited-upon resource becoming available or after a time-out occurs during that wait (if specified when put to sleep). It is mostly used by device drivers waiting for disk or network IO (input/output).
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.
In computer operating systems, a process (or task) may wait for another process to complete its execution. In most systems, a parent process can create an independently executing child process . The parent process may then issue a wait system call , which suspends the execution of the parent process while the child executes.
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.
enter the monitor: enter the method if the monitor is locked add this thread to e block this thread else lock the monitor leave the monitor: schedule return from the method wait c: add this thread to c.q schedule block this thread notify c: if there is a thread waiting on c.q select and remove one thread t from c.q (t is called "the notified ...
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Futexes have two basic operations, WAIT and WAKE. WAIT(addr, val) 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.