4cd18a22d5
followed are: Only 3 functions (pthread_cancel, pthread_setcancelstate, pthread_setcanceltype) are required to be async-signal-safe by POSIX. None of the rest of the pthread api is required to be async-signal-safe. This means that only the three mentioned functions are safe to use from inside signal handlers. However, there are certain system/libc calls that are cancellation points that a caller may call from within a signal handler, and since they are cancellation points calls have to be made into libthr to test for cancellation and exit the thread if necessary. So, the cancellation test and thread exit code paths must be async-signal-safe as well. A summary of the changes follows: o Almost all of the code paths that masked signals, as well as locking the pthread structure now lock only the pthread structure. o Signals are masked (and left that way) as soon as a thread enters pthread_exit(). o The active and dead threads locks now explicitly require that signals are masked. o Access to the isdead field of the pthread structure is protected by both the active and dead list locks for writing. Either one is sufficient for reading. o The thread state and type fields have been combined into one three-state switch to make it easier to read without requiring a lock. It doesn't need a lock for writing (and therefore for reading either) because only the current thread can write to it and it is an integer value. o The thread state field of the pthread structure has been eliminated. It was an unnecessary field that mostly duplicated the flags field, but required additional locking that would make a lot more code paths require signal masking. Any truly unique values (such as PS_DEAD) have been reborn as separate members of the pthread structure. o Since the mutex and condvar pthread functions are not async-signal-safe there is no need to muck about with the wait queues when handling a signal ... o ... which also removes the need for wrapping signal handlers and sigaction(2). o The condvar and mutex async-cancellation code had to be revised as a result of some of these changes, which resulted in semi-unrelated changes which would have been difficult to work on as a separate commit, so they are included as well. The only part of the changes I am worried about is related to locking for the pthread joining fields. But, I will take a closer look at them once this mega-patch is committed.
144 lines
3.2 KiB
C
144 lines
3.2 KiB
C
/*
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* David Leonard <d@openbsd.org>, 1999. Public domain.
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* $FreeBSD$
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*/
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#include <sys/errno.h>
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#include <pthread.h>
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#include <stdlib.h>
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#include "thr_private.h"
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/*
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* Static prototypes
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*/
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static void testcancel(void);
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__weak_reference(_pthread_cancel, pthread_cancel);
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__weak_reference(_pthread_setcancelstate, pthread_setcancelstate);
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__weak_reference(_pthread_setcanceltype, pthread_setcanceltype);
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__weak_reference(_pthread_testcancel, pthread_testcancel);
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/*
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* Posix requires this function to be async-cancel-safe, so it
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* may not aquire any type of resource or call any functions
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* that might do so.
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*/
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int
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_pthread_cancel(pthread_t pthread)
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{
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/* Don't continue if cancellation has already been set. */
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if (atomic_cmpset_int(&pthread->cancellation, (int)CS_NULL,
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(int)CS_PENDING) != 1)
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return (0);
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/*
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* Only wakeup threads that are in cancellation points or
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* have set async cancel.
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* XXX - access to pthread->flags is not safe. We should just
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* unconditionally wake the thread and make sure that
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* the the library correctly handles spurious wakeups.
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*/
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if ((pthread->cancellationpoint || pthread->cancelmode == M_ASYNC) &&
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(pthread->flags & PTHREAD_FLAGS_NOT_RUNNING) != 0)
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PTHREAD_WAKE(pthread);
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return (0);
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}
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/*
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* Posix requires this function to be async-cancel-safe, so it
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* may not aquire any type of resource or call any functions
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* that might do so.
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*/
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int
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_pthread_setcancelstate(int state, int *oldstate)
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{
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int ostate;
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ostate = (curthread->cancelmode == M_OFF) ? PTHREAD_CANCEL_DISABLE :
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PTHREAD_CANCEL_ENABLE;
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switch (state) {
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case PTHREAD_CANCEL_ENABLE:
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curthread->cancelmode = curthread->cancelstate;
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break;
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case PTHREAD_CANCEL_DISABLE:
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if (curthread->cancelmode != M_OFF) {
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curthread->cancelstate = curthread->cancelmode;
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curthread->cancelmode = M_OFF;
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}
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break;
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default:
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return (EINVAL);
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}
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if (oldstate != NULL)
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*oldstate = ostate;
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return (0);
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}
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/*
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* Posix requires this function to be async-cancel-safe, so it
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* may not aquire any type of resource or call any functions that
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* might do so.
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*/
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int
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_pthread_setcanceltype(int type, int *oldtype)
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{
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enum cancel_mode omode;
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omode = curthread->cancelstate;
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switch (type) {
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case PTHREAD_CANCEL_ASYNCHRONOUS:
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if (curthread->cancelmode != M_OFF)
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curthread->cancelmode = M_ASYNC;
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curthread->cancelstate = M_ASYNC;
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break;
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case PTHREAD_CANCEL_DEFERRED:
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if (curthread->cancelmode != M_OFF)
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curthread->cancelmode = M_DEFERRED;
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curthread->cancelstate = M_DEFERRED;
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break;
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default:
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return (EINVAL);
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}
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if (oldtype != NULL) {
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if (omode == M_DEFERRED)
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*oldtype = PTHREAD_CANCEL_DEFERRED;
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else if (omode == M_ASYNC)
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*oldtype = PTHREAD_CANCEL_ASYNCHRONOUS;
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}
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return (0);
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}
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void
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_pthread_testcancel(void)
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{
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testcancel();
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}
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static void
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testcancel()
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{
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if (curthread->cancelmode != M_OFF) {
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/* Cleanup a canceled thread only once. */
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if (atomic_cmpset_int(&curthread->cancellation,
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(int)CS_PENDING, (int)CS_SET) == 1) {
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_thread_exit_cleanup();
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pthread_exit(PTHREAD_CANCELED);
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PANIC("cancel");
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}
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}
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}
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void
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_thread_enter_cancellation_point(void)
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{
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testcancel();
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curthread->cancellationpoint = 1;
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}
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void
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_thread_leave_cancellation_point(void)
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{
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curthread->cancellationpoint = 0;
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testcancel();
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}
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