libs/utils/docs/thpool/FAQ.md - celix - Git at Google


 ### Why isn't pthread_exit() used to exit a thread?
 `thread_do` used to use pthread_exit(). However that resulted in
 hard times of testing for memory leaks. The reason is that on pthread_exit()
 not all memory is freed bt pthread (probably for future threads or false
 belief that the application is terminating). For these reasons a simple return
 is used.

 Interestingly using `pthread_exit()` results in much more memory being allocated.


 ### Why do you use sleep() after calling thpool_destroy()?
 This is needed only in the tests. The reason is that if you call thpool_destroy
 and then exit immediately, maybe the program will exit before all the threads
 had the time to deallocate. In that way it is impossible to check for memory
 leaks.

 In production you don't have to worry about this since if you call exit,
 immediately after you destroyed the pool, the threads will be freed
 anyway by the OS. If you either way destroy the pool in the middle of your
 program it doesn't matter again since the program will not exit immediately
 and thus threads will have more than enough time to terminate.


 ### Why does wait() use all my CPU?
 Normally `wait()` will spike CPU usage to full when called. This is normal as long as it doesn't last for more than 1 second. The reason this happens is that `wait()` goes through various phases of polling (what is called smart polling).

  * Initially there is no interval between polling and hence the 100% use of your CPU.
  * After that the polling interval grows exponentially.
  * Finally after x seconds, if there is still work, polling falls back to a very big interval.

 The reason `wait()` works in this way, is that the function is mostly used when someone wants to wait for some calculation to finish. So if the calculation is assumed to take a long time then we don't want to poll too often. Still we want to poll fast in case the calculation is a simple one. To solve these two problems, this seemingly awkward behaviour is present.

	### Why isn't pthread_exit() used to exit a thread?
	`thread_do` used to use pthread_exit(). However that resulted in
	hard times of testing for memory leaks. The reason is that on pthread_exit()
	not all memory is freed bt pthread (probably for future threads or false
	belief that the application is terminating). For these reasons a simple return
	is used.

	Interestingly using `pthread_exit()` results in much more memory being allocated.


	### Why do you use sleep() after calling thpool_destroy()?
	This is needed only in the tests. The reason is that if you call thpool_destroy
	and then exit immediately, maybe the program will exit before all the threads
	had the time to deallocate. In that way it is impossible to check for memory
	leaks.

	In production you don't have to worry about this since if you call exit,
	immediately after you destroyed the pool, the threads will be freed
	anyway by the OS. If you either way destroy the pool in the middle of your
	program it doesn't matter again since the program will not exit immediately
	and thus threads will have more than enough time to terminate.



	### Why does wait() use all my CPU?
	Normally `wait()` will spike CPU usage to full when called. This is normal as long as it doesn't last for more than 1 second. The reason this happens is that `wait()` goes through various phases of polling (what is called smart polling).

	* Initially there is no interval between polling and hence the 100% use of your CPU.
	* After that the polling interval grows exponentially.
	* Finally after x seconds, if there is still work, polling falls back to a very big interval.

	The reason `wait()` works in this way, is that the function is mostly used when someone wants to wait for some calculation to finish. So if the calculation is assumed to take a long time then we don't want to poll too often. Still we want to poll fast in case the calculation is a simple one. To solve these two problems, this seemingly awkward behaviour is present.