Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Suspending and Resuming Threads

Suspending and Resuming Threads

It can help system performance to delay certain conditional tasks that depend on time-consuming initialization routines or other factors. After all, it is not efficient to enter a loop and check 10,000 times if a required component is finally ready for use. A better approach is to put the worker thread to sleep for an appropriate amount of time, such as 10 milliseconds, check the state of the dependencies after that time, and go back to sleep for another 10 milliseconds or continue processing when conditions permit. Use the Sleep function from within the thread itself to suspend and resume a thread. You can also use the SuspendThread and ResumeThread functions to control a thread through another thread.

The Sleep function accepts a numeric value that specifies the sleep interval in milliseconds. It is important to remember that the actual sleep interval will likely exceed this value. The Sleep function relinquishes the remainder of the current thread's quantum and the scheduler will not give this thread another time slice until the specified interval has passed and there are no other threads with higher priority. For example, the function call sleep(0) does not imply a sleep interval of zero milliseconds. Instead, sleep(0) relinquishes the remainder of the current quantum to other threads. The current thread will only continue to run if the scheduler has no other threads with the same or higher priority on the thread list.

Similar to the sleep(0) call, the SleepTillTick function relinquishes the remainder of the current thread's quantum and suspends the thread until the next system tick. This is useful if you want to synchronize a task on a system tick basis.

The WaitForSingleObject or WaitForMultipleObjects functions suspend a thread until another thread or a synchronization object is signaled. For example, a thread can wait for another thread to exit without having to enter a loop with repeated Sleep and GetExitCodeThread calls if the WaitForSingleObject function is enabled instead. This approach results in a better use of resources and improves code readability. It is possible to pass a timeout value in milliseconds to the WaitForSingleObject or WaitForMultipleObjects functions.

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