CODEWITHSUNDEEP
cmultithreadingpthreadsblocking
A Sedate Mutant
A Sedate Mutant

Reputation: 11

How to gracefully make a blocking pthread exit from the main thread?

I have a pthread which does an indefinite polling on some file descriptors, with negative timeout parameter.

From the main thread, I would like to be able to indicate to the polling thread that it should exit.

I did some research and found the following approaches:

  1. Use pthread_cancel(): This was discouraged as it might lead to unintended consequences of not clearing any held resources or mutexes

  2. Use a variable as a flag and set it in the main thread. The polling thread checks this flag every iteration and if set, exits by calling pthread_exit(). This approach won't work because my polling thread doesn't loop, but simply blocks indefinitely, waiting on the file descriptors.

Can anyone suggest an elegant solution to this problem ?

Thanks! ASM

Upvotes: 1

Views: 548

Answers (2)

n. m. could be an AI
n. m. could be an AI

Reputation: 119847

You can send the blocking thread a signal (e.g. SIGUSR1) with pthread_kill(). The select call should then return a negative value and set errno to EINTR. Don't forget to set a handler for the signal you send.

Upvotes: 1

caf
caf

Reputation: 239011

You can create an anonymous pipe with pipe(2) and have the file-descriptor-watching thread add the read end to its polled file descriptors, exiting when that file descriptor reports EOF. The main thread then just closes the write end when it wants the thread to exit.

Upvotes: 5

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