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Different implementations of events may provide different subsets of these possible operations; for example, the implementation provided by Microsoft Windows provides the operations wait (WaitForObject and related functions), set (SetEvent), and clear (ResetEvent). An option that may be specified during creation of the event object changes the ...
One important caveat of this functionality, however, is that while the code resembles traditional blocking code, the code is actually non-blocking and potentially multithreaded, meaning that many intervening events may occur while waiting for the promise targeted by an await to resolve.
The number of threads may be dynamically adjusted during the lifetime of an application based on the number of waiting tasks. For example, a web server can add threads if numerous web page requests come in and can remove threads when those requests taper down. [disputed – discuss] The cost of having a larger thread pool is increased resource ...
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 ...
Callbacks can be attached which will run in the main thread, thus alleviating the need for complex locking solutions. A prime example of such usage, which comes from Twisted's support libraries, is using this model to call into databases. The database call itself happens on a foreign thread, but the analysis of the result happens in the main ...
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.
In systems that rely on a backoff mechanism (e.g. exponential backoff), the clients will retry failed calls by waiting a specific amount of time between consecutive retries. In order to avoid the thundering herd problem, jitter can be purposefully introduced in order to break the synchronization across the clients, thereby avoiding collisions.
The event loop almost always operates asynchronously with the message originator. When the event loop forms the central control flow construct of a program, as it often does, it may be termed the main loop or main event loop. This title is appropriate, because such an event loop is at the highest level of control within the program.