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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.
On Windows, the Sleep() function takes a single parameter of the number of milliseconds to sleep. The Sleep() function is included in kernel32.dll. [1]The Sleep() function has a resolution no higher than the current timer resolution, typically 16ms but at minimum 1ms, adjustable via the timeBeginPeriod() family of "media timer" APIs.
Because of this, if an interface method needs to return a promise object, but itself does not require await in the body to wait on any asynchronous tasks, it does not need the async modifier either and can instead return a promise object directly.
The time limit for SIGALRM is based on real or clock time; SIGVTALRM is based on CPU time used by the process; and SIGPROF is based on CPU time used by the process and by the system on its behalf (known as a profiling timer). On some systems SIGALRM may be used internally by the implementation of the sleep function. SIGBUS
In some cases, the value t may refer to an upper bound to the time delay, rather than a specific time delay value. The name exponential backoff refers to the exponential growth characteristic of the backoff, rather than an exact numeric relationship between adverse event counts and delay times.
On 5 January 1975, the 12-bit field that had been used for dates in the TOPS-10 operating system for DEC PDP-10 computers overflowed, in a bug known as "DATE75". The field value was calculated by taking the number of years since 1964, multiplying by 12, adding the number of months since January, multiplying by 31, and adding the number of days since the start of the month; putting 2 12 − 1 ...
Likewise, even if consumers are blocked for a long time on processing their current tasks and the queue is full, producers are always busy-waiting. This is a wasteful mechanism. What is needed is a way to make producer threads block until the queue is non-full, and a way to make consumer threads block until the queue is non-empty.
A useful way to think of a semaphore as used in a real-world system is as a record of how many units of a particular resource are available, coupled with operations to adjust that record safely (i.e., to avoid race conditions) as units are acquired or become free, and, if necessary, wait until a unit of the resource becomes available.