dwMilliseconds

dwMilliseconds is a parameter name used in several Win32 API functions to specify a time interval in milliseconds. It is typically defined as a DWORD, an unsigned 32-bit value, and it conveys a duration or timeout in units of one millisecond.

In practice, dwMilliseconds controls how long a function should wait for a condition to occur or for an event to be signaled. It commonly appears in wait-related functions such as WaitForSingleObject and WaitForMultipleObjects, where it represents the maximum amount of time to wait. A value of 0 requests an immediate return, allowing the caller to poll for a condition without blocking. A value of 0xFFFFFFFF is defined as INFINITE for those wait functions, indicating that the call should wait indefinitely until the condition is satisfied or an error occurs.

Other functions also use a parameter named dwMilliseconds with the same general meaning, but the exact interpretation can vary by API. For example, some timing or scheduling APIs may treat the value as a delay or sleep duration rather than a wait timeout. Always refer to the specific function’s documentation to confirm semantics, return values, and error handling for a given dwMilliseconds value.

Common considerations include the practical upper limit of 2^32-1 milliseconds (about 49.7 days) for a single interval, and the need to avoid overflow when converting from larger units (such as seconds) to milliseconds. Because dwMilliseconds is a timer-based value, its behavior may also be affected by system time changes or clock discipline in certain scenarios.