WSAWaitForMultipleEvents

The Windows Sockets WSAWaitForMultipleEvents function returns either when one or all of the specified event objects are in the signaled state, or when the time-out interval expires.

DWORD WSAWaitForMultipleEvents(

DWORD cEvents,
const WSAEVENT FAR *lphEvents,
BOOL fWaitAll,
DWORD dwTimeOUT,
BOOL fAlertable
);

Parameters

cEvents

[in] Specifies the number of event object handles in the array pointed to by lphEvents. The maximum number of event object handles is WSA_MAXIMUM_WAIT_EVENTS. One or more events must be specified.

lphEvents

[in] Points to an array of event object handles.

fWaitAll

[in] Specifies the wait type. If TRUE, the function returns when all event objects in the lphEvents array are signaled at the same time. If FALSE, the function returns when any one of the event objects is signaled. In the latter case, the return value indicates the event object whose state caused the function to return.

dwTimeout

[in] Specifies the time-out interval, in milliseconds. The function returns if the interval expires, even if conditions specified by the fWaitAll parameter are not satisfied. If dwTimeout is zero, the function tests the state of the specified event objects and returns immediately. If dwTimeout is WSA_INFINITE, the function's time-out interval never expires.

fAlertable

[in] Specifies whether the function returns when the system queues an I/O completion routine for execution by the calling thread. If TRUE, the completion routine is executed and the function returns. If FALSE, the completion routine is not executed when the function returns.

Remarks

The WSAWaitForMultipleEvents function returns either when any one or when all of the specified objects are in the signaled state, or when the time-out interval elapses. This function is also used to perform an alertable wait by setting the parameter fAltertable to be TRUE. This enables the function to return when the system queues an I/O completion routine to be executed by the calling thread.

When fWaitAll is TRUE, the function's wait condition is satisfied only when the state of all objects is signaled at the same time. The function does not modify the state of the specified objects until all objects are simultaneously signaled.

Applications that simply need to enter an alertable wait state without waiting for any event objects to be signalled should use the Win32 sleepEx function.

Return Values

If the function succeeds, the return value indicates the event object that caused the function to return.

If the function fails, the return value is WSA_WAIT_FAILED. To get extended error information, call WSAGetLastError.

The return value upon success is one of the following values:

Value	Meaning
WSA_WAIT_EVENT_0 to (WSA_WAIT_EVENT_0 + cEvents - 1)	If fWaitAll is TRUE, the return value indicates that the state of all specified event objects is signaled. If fWaitAll is FALSE, the return value minus WSA_WAIT_EVENT_0 indicates the lphEvents array index of the object that satisfied the wait.
WAIT_IO_COMPLETION	One or more I/O completion routines are queued for execution.
WSA_WAIT_TIMEOUT	The time-out interval elapsed and the conditions specified by the fWaitAll parameter are not satisfied.

Error Codes

WSANOTINITIALISED	A successful WSAStartup must occur before using this function.
WSAENETDOWN	The network subsystem has failed.
WSAEINPROGRESS	A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSA_NOT_ENOUGH_MEMORY	Not enough free memory available to complete the operation.
WSA_INVALID_HANDLE	One or more of the values in the lphEvents array is not a valid event object handle.
WSA_INVALID_PARAMETER	The cEvents parameter does not contain a valid handle count.

See Also

WSACloseEvent, WSACreateEvent

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