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I've created a multi-threaded application using C++ and POSIX threads. In which I should now block a thread (main thread) until a boolean flag is set (becomes true).
I've found two ways to get this done.
Spinning through a loop without sleep.
while(!flag);
Spinning through a loop with sleep.
while(!flag){
sleep(some_int);
}
If I should follow the first way, why do some people write codes following the second way? If the second way should be used, why should we make current thread to sleep? And what are disadvantages of this way?
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Thread. sleep is bad! It blocks the current thread and renders it unusable for further work.
Sleep method. Calling the Thread. Sleep method causes the current thread to immediately block for the number of milliseconds or the time interval you pass to the method, and yields the remainder of its time slice to another thread.
Using Thread. sleep() frequently in an automation framework is not a good practice. If the applied sleep is of 5 secs and the web element is displayed in 2 secs only, the extra 3 secs will increase the execution time. And if you use it more often in the framework, the execution time would increase drastically.
Wait() method releases lock during Synchronization. Sleep() method does not release the lock on object during Synchronization. Wait() should be called only from Synchronized context. There is no need to call sleep() from Synchronized context.
The first option (a "busy wait") wastes an entire core for the duration of the wait, preventing other useful work being done and/or wasting energy.
The second option is less wasteful - your waiting thread uses very little CPU and allows other threads to run. But it is still wasteful to keep switching back to the thread to check the flag.
Far better than either would be to use a condition variable, which allows the waiting thread to block without consuming any resources until it is able to proceed.
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