Author: Eugene Nalimov
Date: 17:26:51 04/24/01
Go up one level in this thread
On April 24, 2001 at 20:07:30, Robert Hyatt wrote: >On April 24, 2001 at 17:24:51, Hristo wrote: > >>On April 24, 2001 at 16:51:38, Vincent Diepeveen wrote: >> >>>On April 24, 2001 at 16:18:01, Hristo wrote: >>> >>>>On April 24, 2001 at 13:15:00, Vincent Diepeveen wrote: >>>> >>>>>Hello, >>>>> >>>>>I'm looking for code to make events in linux. >>>>> >>>>>In windows i use functions like >>>>> WaitForMultipleObjects() >>>> >>>>There isn't one! If you depend on this functionality >>>>you migth have to redesign (rethink) something. >>>>Look for conditional variables ... >>>>In general you need the services of pthreads library ... >>>>look for ... >>>>pthread_cond_init >>>>pthread_cond_wait >>>>pthread_cond_*, etc ... >>>>... >>>>pthread_mutex_init >>>>pthread_mutex_lock // no time out >>>>pthread_mutex_*, etc ... >>> >>>I see so i go write myself this function then :) >> >>duhhhh ... yep. Well maybe someone wrote it already. >>If you would use it I will take a crack at it tonight >>and send it to you. >>If anyone knows about possible implementation of this >>function WaitForMultipleObjects ... >>... yell YELL now ... cause it is a hairy bastard! >> >>hristo >> > > >What exactly does it do? The WaitForMultipleObjects function returns when one of the following occurs: * Either any one or all of the specified objects are in the signaled state. * The time-out interval elapses. DWORD WaitForMultipleObjects( DWORD nCount, // number of handles in the handle array CONST HANDLE *lpHandles, // pointer to the object-handle array BOOL fWaitAll, // wait flag DWORD dwMilliseconds // time-out interval in milliseconds ); Parameters nCount -- Specifies the number of object handles in the array pointed to by lpHandles. The maximum number of object handles is MAXIMUM_WAIT_OBJECTS. lpHandles -- Pointer to an array of object handles. For a list of the object types whose handles can be specified, see the following Remarks section. The array can contain handles of objects of different types. Windows NT: The handles must have SYNCHRONIZE access. For more information, see Standard Access Rights. Windows 95: No handle may be a duplicate of another handle created using DuplicateHandle. fWaitAll -- Specifies the wait type. If TRUE, the function returns when the state all objects in the lpHandles array is signaled. If FALSE, the function returns when the state of any one of the objects set to is signaled. In the latter case, the return value indicates the object whose state caused the function to return. dwMilliseconds -- Specifies the time-out interval, in milliseconds. The function returns if the interval elapses, even if the conditions specified by the bWaitAll parameter are not met. If dwMilliseconds is zero, the function tests the states of the specified objects and returns immediately. If dwMilliseconds is INFINITE, the function's time-out interval never elapses. Return Values If the function succeeds, the return value indicates the event that caused the function to return. This value can be one of the following. Value Meaning WAIT_OBJECT_0 to (WAIT_OBJECT_0 + nCount – 1) If bWaitAll is TRUE, the return value indicates that the state of all specified objects is signaled. If bWaitAll is FALSE, the return value minus WAIT_OBJECT_0 indicates the lpHandles array index of the object that satisfied the wait. If more than one object became signalled during the call, this is the array index of the signalled object with the smallest index value of all the signalled objects. WAIT_ABANDONED_0 to (WAIT_ABANDONED_0 + nCount – 1) If bWaitAll is TRUE, the return value indicates that the state of all specified objects is signaled and at least one of the objects is an abandoned mutex object. If bWaitAll is FALSE, the return value minus WAIT_ABANDONED_0 indicates the lpHandles array index of an abandoned mutex object that satisfied the wait. WAIT_TIMEOUT The time-out interval elapsed and the conditions specified by the bWaitAll parameter are not satisfied. If the function fails, the return value is WAIT_FAILED. To get extended error information, call GetLastError. Remarks The WaitForMultipleObjects function determines whether the wait criteria have been met. If the criteria have not been met, the calling thread enters an efficient wait state, consuming very little processor time while waiting for the criteria to be met. When fWaitAll is TRUE, the function's wait operation is completed only when the states of all objects have been set to signaled. The function does not modify the states of the specified objects until the states of all objects have been set to signaled. For example, a mutex can be signaled, but the thread does not get ownership until the states of the other objects are also set to signaled. In the meantime, some other thread may get ownership of the mutex, thereby setting its state to nonsignaled. Before returning, a wait function modifies the state of some types of synchronization objects. Modification occurs only for the object or objects whose signaled state caused the function to return. For example, the count of a semaphore object is decreased by one. When fWaitAll is FALSE, and multiple objects are in the signaled state, the function chooses one of the objects to satisfy the wait; the states of the objects not selected are unaffected. The WaitForMultipleObjects function can specify handles of any of the following object types in the lpHandles array: * Change notification * Console input * Event * Job * Mutex * Process * Semaphore * Thread * Waitable timer For more information, see Synchronization Objects. Use caution when calling the wait functions and code that directly or indirectly creates windows. If a thread creates any windows, it must process messages. Message broadcasts are sent to all windows in the system. A thread that uses a wait function with no time-out interval may cause the system to become deadlocked. Two examples of code that indirectly creates windows are DDE and COM CoInitialize. Therefore, if you have a thread that creates windows, use MsgWaitForMultipleObjects or MsgWaitForMultipleObjectsEx, rather than WaitForMultipleObjects. > >>> >>>>keep in mind that there is no function to wait on multiple >>>>conditional variables for you. Which makes it difficult when >>>>you need to wait on several things to happen before continue. >>>> >>>>Also semaphores do not have a time-out and neither do mutexes, >>>>so you have to couple a mutex+conditional_variable to be able to lock >>>>something with a time out. I've spend some time making things >>>>work so I have classes that encapsulate some of these and are >>>>prety simple. I can send them to you if you want ... >>>>my e-mail address is donquixote@pacbell.net >>>>(it changed but I'm not sure who can fix it for me on this message board) >>>> >>>>WaitForMultipleObjects is best implemented by the OS (kuddos to MS), >>>>however it is possible to write it using pthreads. >>>> >>>> >>>>best regards. >>>>hristo >>>> >>>>> >>>>>but i can't find the equivalent of this for linux! >>>>> >>>>>Best regards, >>>>>Vincent
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