Why Does Sleep(1) Seem to Sleep for 15ms in Windows?

Sleep() Function Behavior in Windows

When calling the Sleep() function, a thread typically suspends execution for the specified duration. However, in some cases, it may seem that the thread sleeps for a longer period.

In Windows versions such as Windows 7, Sleep() operates on a time quantum. This means that any non-zero delay is rounded up to the nearest quantum, which may result in slightly longer sleep durations.

A common symptom of this behavior is that a call to Sleep(1) may actually cause a sleep of around 15ms. This is because the operating system scheduler typically uses a quantum of 15.6ms.

To illustrate this, a code snippet is provided:

<code class="cpp">#include <iostream>
#include <ctime>
#include <windows.h>

void test(void)
{
    std::cout <p>If executed on Windows 7, this code will likely report sleep durations around 15ms instead of 1ms.</p>
<p>Therefore, it's typical behavior for Sleep() to sleep for a slightly longer period than the specified delay due to the time quantum system employed by Windows.</p></windows.h></ctime></iostream></code>

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