CODEWITHSUNDEEP
c++multithreading
YNotSayNay
YNotSayNay

Reputation: 35

How to know when to kill threads?

I'm designing a thread library. So far I have a method that initializes the library, one that creates threads, and one that yields the current thread to the next one on a queue of ready threads.

Before I move on to implementing semaphores for the threads, I figured I should probably kill the threads as soon as they are done and free up their allocated memory, but I'm having trouble figuring out how to do that. How do I tell when a thread has "finished"?

Upvotes: 3

Views: 217

Answers (3)

Martin James
Martin James

Reputation: 24897

The best policy, by far, for killing threads is to not explicitly do it, (unless you are an OS, ie. on app shutdown). Queue messages and tasks to threads that loop around some queue to perform more work. If you don't write any code to continually new, create, start, terminate, delete, test, check, enlist, delist, enqueue, dequeue and otherwise micro-manage threads, then that code cannot contain bugs.

Upvotes: 0

justin
justin

Reputation: 104698

You don't just kill threads safely or reliably -- let them exit naturally (when their entry returns).

Although the system provides a means to kill the thread, nearly any C++ program out there could expect undefined behavior if it were to continue. You could dream up cases where killing could be accomplished without side effects (to the rest of the program), but that program does not at all resemble idiomatic C++. Such a program would be very exotic, with many unusual and severe restrictions.

When you want to known when a thread has exited or not, you can add some cleanup before it exits in order to track its status.

When you want the ability to request a thread exit (naturally), consider run loops and messages.

Upvotes: 4

vvnraman
vvnraman

Reputation: 1343

You don't explicitly kill the threads when they are finished running their forked procedures as the code which would be doing that would still be in the context of the thread to be killed.

You have a scheduler/interrupt handler which handles the context switching of the threads and maintains a few queues for managing this. You can have it save a reference to to the threads to be killed, something like scheduler->SetThreadToKill( currentThread ); inside probably your finish() method (or similar), which sets a flag for the corresponding threads.

When a context switch occurs, and you have swapped out all data structures of the current thread with that of the next thread, you scheduler can call the destructor for all the threads which have the toBeKilled flag set.

Upvotes: 0

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