Advanced Programming in the UNIX® Environment

ptg10805159

Section 21.5 Source Code 829

520 /*

521 * Cancellation routine for the worker thread.

522 *

523 * LOCKING: acquires and releases workerlock.

524 */

525 void

526 client_cleanup(void *arg)

527 {

528 struct worker_thread *wtp;

529 pthread_t tid;

530 tid=(pthread_t)((long)arg);

531 pthread_mutex_lock(&workerlock);

532 for (wtp = workers; wtp != NULL; wtp = wtp->next) {

533 if (wtp->tid == tid) {

534 if (wtp->next != NULL)

535 wtp->next->prev=wtp->prev;

536 if (wtp->prev != NULL)

537 wtp->prev->next=wtp->next;

538 else

539 workers=wtp->next;

540 break;

541 }

542 }

543 pthread_mutex_unlock(&workerlock);

544 if (wtp != NULL) {

545 close(wtp->sockfd);

546 free(wtp);

547 }

548 }

[520 – 542] The client_cleanup function is the thread cleanup handler for the

worker threads that communicate with client commands. This function is

called when the thread callspthread_exit,callspthread_cleanup_pop

with a nonzeroargument, or responds to a cancellation request. The

argument is the thread ID of the thread terminating.

We lock theworkerlockmutex and search the list of worker threads until

we find a matching thread ID. When we find a match, we remove the

worker thread structurefromthe list and stop the search.

[543 – 548] We unlock theworkerlockmutex, close the socket file descriptor used by

the thread to communicate with the client, and free the memory backing the

worker_threadstructure.

Since we try to acquiretheworkerlock mutex, if a thread reaches a

cancellation point while thekill_workersfunction is still walking the list,

we will have to wait untilkill_workersreleases the mutex before we can

proceed.