user-0 提问: 等待某个条件一定时间后，如果条件不满足就退出等待，要怎么写

回复:
user: user-1
content: 如果while小括号里的函数不是异步的，那就会一直等下去。 按5l的方法用中断吧。

user: user-2
content: linux核心有schdule_timeout();

user: user-3
content: 单片机，可以使用外部中断，定时器中断。 需要控制时间，用定时器，需要获取外部数据用中断。

user: user-4
content: 小心time_cnt是负数！

user: user-5
content: 如果输入引脚电平能触发中断，可以使用中断来处理，但如果等待时间比较短，中间也没什么工作要做时，还是死等简单可靠。

user: user-0
content: 我就一写写单片机的，这些我压根就不知所云

user: user-4
content: 《Windows核心编程》 WaitForSingleObject The WaitForSingleObject function returns when one of the following occurs:   The specified object is in the signaled state.  The time-out interval elapses.  DWORD WaitForSingleObject(   HANDLE hHandle,        // handle to object to wait for   DWORD dwMilliseconds   // time-out interval in milliseconds );   Parameters hHandle  Handle to the object. For a list of the object types whose handles can be specified, see the following Remarks section.  Windows NT: The handle must have SYNCHRONIZE access. For more information, see Standard Access Rights.   dwMilliseconds  Specifies the time-out interval, in milliseconds. The function returns if the interval elapses, even if the object's state is nonsignaled. If dwMilliseconds is zero, the function tests the object's state 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_ABANDONED The specified object is a mutex object that was not released by the thread that owned the mutex object before the owning thread terminated. Ownership of the mutex object is granted to the calling thread, and the mutex is set to nonsignaled.  WAIT_OBJECT_0 The state of the specified object is signaled.  WAIT_TIMEOUT The time-out interval elapsed, and the object's state is nonsignaled.    If the function fails, the return value is WAIT_FAILED. To get extended error information, call GetLastError.   Remarks The WaitForSingleObject function checks the current state of the specified object. If the object's state is nonsignaled, the calling thread enters an efficient wait state. The thread consumes very little processor time while waiting for the object state to become signaled or the time-out interval to elapse.  Before returning, a wait function modifies the state of some types of synchronization objects. Modification occurs only for the object whose signaled state caused the function to return. For example, the count of a semaphore object is decreased by one.   The WaitForSingleObject function can wait for the following objects:   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 WaitForSingleObject.  Windows CE: Windows CE does not support waiting for semaphores, change notification objects, console input, and timers.  Waiting on an invalid handle causes WaitForSingleObject to return WAIT_FAILED.  QuickInfo   Windows NT: Requires version 3.1 or later.   Windows: Requires Windows 95 or later.   Windows CE: Requires version 1.0 or later.   Header: Declared in winbase.h.   Import Library: Use kernel32.lib.  See Also Synchronization Overview, Synchronization Functions, CancelWaitableTimer, CreateEvent, CreateFile, CreateMutex, CreateProcess, CreateRemoteThread, CreateSemaphore, CreateThread, CreateWaitableTimer, FindFirstChangeNotification, GetStdHandle, MsgWaitForMultipleObjects, MsgWaitForMultipleObjectsEx, OpenEvent, OpenMutex, OpenProcess, OpenSemaphore, OpenWaitableTimer, PulseEvent, ResetEvent, SetEvent, SetWaitableTimer

user: user-6
content: linux下可以使用pthread_cond_timedwait, 如果没有pthread支持的单片机那肯定是while死循环+sleep检查了。