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copied!<p>Well, in fact all these explainations are congruent.</p> <p>The most simplified (and hence not 100% accurate) explaination of an event is to see an event as kind of a flag service provided by the operating system. A signaled Event can be seen as a set flag, an unsignalled event on the other hand can be seen as an unset flag.</p> <p>For implementing a producer/consumer thread-system based on flags, you usually do something like the following (note for the sake of simplicity i neglect further synchronization mechanisms):</p> <pre><code>static volatile int flag = 0; static volatile char data = 'A'; // Some code to initialize the threads void producer() { while (1) { Sleep(1000); data++; flag = 1; } } void consumer() { while (1) { /* Busy wait for the occurence of more data */ while (!flag) { // wait for next data } flag = 0; // process data } } </code></pre> <p>Unluckily this would lead to a waste of processor cycles in the busy wait loop or unwanted deferral of execution due to a <code>Sleep</code> call introduced to lower the CPU consumption. Both is unwanted.</p> <p>In order to avoid such problems with task synchronization, operating systems provide different flag like mechanisms (e.g. Events in Windows). With events, setting and resetting a flag is done by the OS calls <code>SetEvent</code>/<code>ResetEvent</code>. To check for a flag you can use <code>WaitForSingleObject</code>. This call has the power to put a task to sleep until the event is signalled which is optimal in terms of CPU consumption. </p> <p>This turns the above example into something like this:</p> <pre><code>static volatile char data = 'A'; static HANDLE newDataEvent = INVALID_HANDLE_VALUE; // Some code to initialize the threads and the newDataEvent handle void producer() { while (1) { Sleep(1000); data++; SetEvent(newDataEvent); } } void consumer() { while (1) { if (WaitForSingleObject(newDataEvent, INFINITE) == WAIT_OBJECT_0) { ResetEvent(newDataEvent); // process data } } } </code></pre>

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