diff options
Diffstat (limited to 'linuxthreads')
| -rw-r--r-- | linuxthreads/ChangeLog | 18 | ||||
| -rw-r--r-- | linuxthreads/cancel.c | 44 | ||||
| -rw-r--r-- | linuxthreads/condvar.c | 324 | ||||
| -rw-r--r-- | linuxthreads/internals.h | 40 | ||||
| -rw-r--r-- | linuxthreads/join.c | 48 | ||||
| -rw-r--r-- | linuxthreads/oldsemaphore.c | 24 | ||||
| -rw-r--r-- | linuxthreads/pthread.c | 66 | ||||
| -rw-r--r-- | linuxthreads/queue.h | 5 | ||||
| -rw-r--r-- | linuxthreads/restart.h | 35 | ||||
| -rw-r--r-- | linuxthreads/rwlock.c | 2 | ||||
| -rw-r--r-- | linuxthreads/semaphore.c | 54 | ||||
| -rw-r--r-- | linuxthreads/spinlock.c | 24 | ||||
| -rw-r--r-- | linuxthreads/spinlock.h | 28 |
13 files changed, 610 insertions, 102 deletions
diff --git a/linuxthreads/ChangeLog b/linuxthreads/ChangeLog index 37be0e8..78e8552 100644 --- a/linuxthreads/ChangeLog +++ b/linuxthreads/ChangeLog @@ -1,3 +1,21 @@ +2000-01-03 Kaz Kylheku <kaz@ashi.footprints.net> + + Redesigned how cancellation unblocks a thread from internal + cancellation points (sem_wait, pthread_join, + pthread_cond_{wait,timedwait}). + Cancellation won't eat a signal in any of these functions + (*required* by POSIX and Single Unix Spec!). + * condvar.c: spontaneous wakeup on pthread_cond_timedwait won't eat a + simultaneous condition variable signal (not required by POSIX + or Single Unix Spec, but nice). + * spinlock.c: __pthread_lock queues back any received restarts + that don't belong to it instead of assuming ownership of lock + upon any restart; fastlock can no longer be acquired by two threads + simultaneously. + * restart.h: restarts queue even on kernels that don't have + queued real time signals (2.0, early 2.1), thanks to atomic counter, + avoiding a rare race condition in pthread_cond_timedwait. + 1999-12-31 Andreas Jaeger <aj@suse.de> * internals.h: Remove duplicate prototype declarations. diff --git a/linuxthreads/cancel.c b/linuxthreads/cancel.c index c45cac9..8fd8c1e 100644 --- a/linuxthreads/cancel.c +++ b/linuxthreads/cancel.c @@ -52,16 +52,54 @@ int pthread_cancel(pthread_t thread) { pthread_handle handle = thread_handle(thread); int pid; + int dorestart = 0; + pthread_descr th; + pthread_extricate_if *pextricate; __pthread_lock(&handle->h_lock, NULL); if (invalid_handle(handle, thread)) { __pthread_unlock(&handle->h_lock); return ESRCH; } - handle->h_descr->p_canceled = 1; - pid = handle->h_descr->p_pid; + + th = handle->h_descr; + + if (th->p_canceled) { + __pthread_unlock(&handle->h_lock); + return 0; + } + + pextricate = th->p_extricate; + th->p_canceled = 1; + pid = th->p_pid; + + /* If the thread has registered an extrication interface, then + invoke the interface. If it returns 1, then we succeeded in + dequeuing the thread from whatever waiting object it was enqueued + with. In that case, it is our responsibility to wake it up. + And also to set the p_woken_by_cancel flag so the woken thread + can tell that it was woken by cancellation. */ + + if (pextricate != NULL) { + dorestart = pextricate->pu_extricate_func(pextricate->pu_object, th); + th->p_woken_by_cancel = dorestart; + } + __pthread_unlock(&handle->h_lock); - kill(pid, __pthread_sig_cancel); + + /* If the thread has suspended or is about to, then we unblock it by + issuing a restart, instead of a cancel signal. Otherwise we send + the cancel signal to unblock the thread from a cancellation point, + or to initiate asynchronous cancellation. The restart is needed so + we have proper accounting of restarts; suspend decrements the thread's + resume count, and restart() increments it. This also means that suspend's + handling of the cancel signal is obsolete. */ + + if (dorestart) + restart(th); + else + kill(pid, __pthread_sig_cancel); + return 0; } diff --git a/linuxthreads/condvar.c b/linuxthreads/condvar.c index 2ea7513..87a93a9 100644 --- a/linuxthreads/condvar.c +++ b/linuxthreads/condvar.c @@ -25,6 +25,22 @@ #include "queue.h" #include "restart.h" +static int pthread_cond_timedwait_relative_old(pthread_cond_t *, + pthread_mutex_t *, const struct timespec *); + +static int pthread_cond_timedwait_relative_new(pthread_cond_t *, + pthread_mutex_t *, const struct timespec *); + +static int (*pthread_cond_tw_rel)(pthread_cond_t *, pthread_mutex_t *, + const struct timespec *) = pthread_cond_timedwait_relative_old; + +/* initialize this module */ +void __pthread_init_condvar(int rt_sig_available) +{ + if (rt_sig_available) + pthread_cond_tw_rel = pthread_cond_timedwait_relative_new; +} + int pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *cond_attr) { @@ -39,54 +55,125 @@ int pthread_cond_destroy(pthread_cond_t *cond) return 0; } +/* Function called by pthread_cancel to remove the thread from + waiting on a condition variable queue. */ + +static int cond_extricate_func(void *obj, pthread_descr th) +{ + volatile pthread_descr self = thread_self(); + pthread_cond_t *cond = obj; + int did_remove = 0; + + __pthread_lock(&cond->__c_lock, self); + did_remove = remove_from_queue(&cond->__c_waiting, th); + __pthread_unlock(&cond->__c_lock); + + return did_remove; +} + int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex) { volatile pthread_descr self = thread_self(); + pthread_extricate_if extr; + int already_canceled = 0; + + /* Set up extrication interface */ + extr.pu_object = cond; + extr.pu_extricate_func = cond_extricate_func; + + /* Register extrication interface */ + __pthread_set_own_extricate_if(self, &extr); + + /* Atomically enqueue thread for waiting, but only if it is not + canceled. If the thread is canceled, then it will fall through the + suspend call below, and then call pthread_exit without + having to worry about whether it is still on the condition variable queue. + This depends on pthread_cancel setting p_canceled before calling the + extricate function. */ __pthread_lock(&cond->__c_lock, self); - enqueue(&cond->__c_waiting, self); + if (!(THREAD_GETMEM(self, p_canceled) + && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) + enqueue(&cond->__c_waiting, self); + else + already_canceled = 1; __pthread_unlock(&cond->__c_lock); + + if (already_canceled) { + __pthread_set_own_extricate_if(self, 0); + pthread_exit(PTHREAD_CANCELED); + } + pthread_mutex_unlock(mutex); - suspend_with_cancellation(self); - pthread_mutex_lock(mutex); - /* This is a cancellation point */ - if (THREAD_GETMEM(self, p_canceled) + + suspend(self); + __pthread_set_own_extricate_if(self, 0); + + /* Check for cancellation again, to provide correct cancellation + point behavior */ + + if (THREAD_GETMEM(self, p_woken_by_cancel) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { - /* Remove ourselves from the waiting queue if we're still on it */ - __pthread_lock(&cond->__c_lock, self); - remove_from_queue(&cond->__c_waiting, self); - __pthread_unlock(&cond->__c_lock); + THREAD_SETMEM(self, p_woken_by_cancel, 0); + pthread_mutex_lock(mutex); pthread_exit(PTHREAD_CANCELED); } + + pthread_mutex_lock(mutex); return 0; } +/* The following function is used on kernels that don't have rt signals. + SIGUSR1 is used as the restart signal. The different code is needed + because that ordinary signal does not queue. */ + static int -pthread_cond_timedwait_relative(pthread_cond_t *cond, +pthread_cond_timedwait_relative_old(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec * reltime) { volatile pthread_descr self = thread_self(); sigset_t unblock, initial_mask; - int retsleep; + int retsleep, already_canceled, was_signalled; sigjmp_buf jmpbuf; + pthread_extricate_if extr; + +requeue_and_wait_again: - /* Wait on the condition */ + retsleep = 0; + already_canceled = 0; + was_signalled = 0; + + /* Set up extrication interface */ + extr.pu_object = cond; + extr.pu_extricate_func = cond_extricate_func; + + /* Register extrication interface */ + __pthread_set_own_extricate_if(self, &extr); + + /* Enqueue to wait on the condition and check for cancellation. */ __pthread_lock(&cond->__c_lock, self); - enqueue(&cond->__c_waiting, self); + if (!(THREAD_GETMEM(self, p_canceled) + && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) + enqueue(&cond->__c_waiting, self); + else + already_canceled = 1; __pthread_unlock(&cond->__c_lock); + + if (already_canceled) { + __pthread_set_own_extricate_if(self, 0); + pthread_exit(PTHREAD_CANCELED); + } + pthread_mutex_unlock(mutex); - continue_waiting: - /* Set up a longjmp handler for the restart and cancel signals */ - if (sigsetjmp(jmpbuf, 1) == 0) { - THREAD_SETMEM(self, p_signal_jmp, &jmpbuf); - THREAD_SETMEM(self, p_cancel_jmp, &jmpbuf); - THREAD_SETMEM(self, p_signal, 0); - /* Check for cancellation */ - if (THREAD_GETMEM(self, p_canceled) - && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { - retsleep = -1; - } else { + + if (atomic_decrement(&self->p_resume_count) == 0) { + /* Set up a longjmp handler for the restart signal, unblock + the signal and sleep. */ + + if (sigsetjmp(jmpbuf, 1) == 0) { + THREAD_SETMEM(self, p_signal_jmp, &jmpbuf); + THREAD_SETMEM(self, p_signal, 0); /* Unblock the restart signal */ sigemptyset(&unblock); sigaddset(&unblock, __pthread_sig_restart); @@ -95,37 +182,180 @@ pthread_cond_timedwait_relative(pthread_cond_t *cond, retsleep = __libc_nanosleep(reltime, NULL); /* Block the restart signal again */ sigprocmask(SIG_SETMASK, &initial_mask, NULL); + was_signalled = 0; + } else { + retsleep = -1; + was_signalled = 1; } - } else { - retsleep = -1; + THREAD_SETMEM(self, p_signal_jmp, NULL); } - THREAD_SETMEM(self, p_signal_jmp, NULL); - THREAD_SETMEM(self, p_cancel_jmp, NULL); - /* Here, either the condition was signaled (self->p_signal != 0) - or we got canceled (self->p_canceled != 0) - or the timeout occurred (retsleep == 0) - or another interrupt occurred (retsleep == -1) */ - /* This is a cancellation point */ - if (THREAD_GETMEM(self, p_canceled) + + /* Now was_signalled is true if we exited the above code + due to the delivery of a restart signal. In that case, + we know we have been dequeued and resumed and that the + resume count is balanced. Otherwise, there are some + cases to consider. First, try to bump up the resume count + back to zero. If it goes to 1, it means restart() was + invoked on this thread. The signal must be consumed + and the count bumped down and everything is cool. + Otherwise, no restart was delivered yet, so we remove + the thread from the queue. If this succeeds, it's a clear + case of timeout. If we fail to remove from the queue, then we + must wait for a restart. */ + + if (!was_signalled) { + if (atomic_increment(&self->p_resume_count) != -1) { + __pthread_wait_for_restart_signal(self); + atomic_decrement(&self->p_resume_count); /* should be zero now! */ + } else { + int was_on_queue; + __pthread_lock(&cond->__c_lock, self); + was_on_queue = remove_from_queue(&cond->__c_waiting, self); + __pthread_unlock(&cond->__c_lock); + + if (was_on_queue) { + __pthread_set_own_extricate_if(self, 0); + pthread_mutex_lock(mutex); + + if (retsleep == 0) + return ETIMEDOUT; + /* Woken by a signal: resume waiting as + required by Single Unix Specification. */ + goto requeue_and_wait_again; + } + + suspend(self); + } + } + + __pthread_set_own_extricate_if(self, 0); + + /* The remaining logic is the same as in other cancellable waits, + such as pthread_join sem_wait or pthread_cond wait. */ + + if (THREAD_GETMEM(self, p_woken_by_cancel) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { - __pthread_lock(&cond->__c_lock, self); - remove_from_queue(&cond->__c_waiting, self); - __pthread_unlock(&cond->__c_lock); + THREAD_SETMEM(self, p_woken_by_cancel, 0); pthread_mutex_lock(mutex); pthread_exit(PTHREAD_CANCELED); } - /* If not signaled: also remove ourselves and return an error code, but - only if the timeout has elapsed. If not, just continue waiting. */ - if (THREAD_GETMEM(self, p_signal) == 0) { - if (retsleep != 0) - goto continue_waiting; + + pthread_mutex_lock(mutex); + return 0; +} + +/* The following function is used on new (late 2.1 and 2.2 and higher) kernels + that have rt signals which queue. */ + +static int +pthread_cond_timedwait_relative_new(pthread_cond_t *cond, + pthread_mutex_t *mutex, + const struct timespec * reltime) +{ + volatile pthread_descr self = thread_self(); + sigset_t unblock, initial_mask; + int retsleep, already_canceled, was_signalled; + sigjmp_buf jmpbuf; + pthread_extricate_if extr; + + requeue_and_wait_again: + + retsleep = 0; + already_canceled = 0; + was_signalled = 0; + + /* Set up extrication interface */ + extr.pu_object = cond; + extr.pu_extricate_func = cond_extricate_func; + + /* Register extrication interface */ + __pthread_set_own_extricate_if(self, &extr); + + /* Enqueue to wait on the condition and check for cancellation. */ + __pthread_lock(&cond->__c_lock, self); + if (!(THREAD_GETMEM(self, p_canceled) + && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) + enqueue(&cond->__c_waiting, self); + else + already_canceled = 1; + __pthread_unlock(&cond->__c_lock); + + if (already_canceled) { + __pthread_set_own_extricate_if(self, 0); + pthread_exit(PTHREAD_CANCELED); + } + + pthread_mutex_unlock(mutex); + + /* Set up a longjmp handler for the restart signal, unblock + the signal and sleep. */ + + if (sigsetjmp(jmpbuf, 1) == 0) { + THREAD_SETMEM(self, p_signal_jmp, &jmpbuf); + THREAD_SETMEM(self, p_signal, 0); + /* Unblock the restart signal */ + sigemptyset(&unblock); + sigaddset(&unblock, __pthread_sig_restart); + sigprocmask(SIG_UNBLOCK, &unblock, &initial_mask); + /* Sleep for the required duration */ + retsleep = __libc_nanosleep(reltime, NULL); + /* Block the restart signal again */ + sigprocmask(SIG_SETMASK, &initial_mask, NULL); + was_signalled = 0; + } else { + retsleep = -1; + was_signalled = 1; + } + THREAD_SETMEM(self, p_signal_jmp, NULL); + + /* Now was_signalled is true if we exited the above code + due to the delivery of a restart signal. In that case, + everything is cool. We have been removed from the queue + by the other thread, and consumed its signal. + + Otherwise we this thread woke up spontaneously, or due to a signal other + than restart. The next thing to do is to try to remove the thread + from the queue. This may fail due to a race against another thread + trying to do the same. In the failed case, we know we were signalled, + and we may also have to consume a restart signal. */ + + if (!was_signalled) { + int was_on_queue; + + /* __pthread_lock will queue back any spurious restarts that + may happen to it. */ + __pthread_lock(&cond->__c_lock, self); - remove_from_queue(&cond->__c_waiting, self); + was_on_queue = remove_from_queue(&cond->__c_waiting, self); __pthread_unlock(&cond->__c_lock); + + if (was_on_queue) { + __pthread_set_own_extricate_if(self, 0); + pthread_mutex_lock(mutex); + + if (retsleep == 0) + return ETIMEDOUT; + /* Woken by a signal: resume waiting as + required by Single Unix Specification. */ + goto requeue_and_wait_again; + } + + /* Eat the outstanding restart() from the signaller */ + suspend(self); + } + + __pthread_set_own_extricate_if(self, 0); + + /* The remaining logic is the same as in other cancellable waits, + such as pthread_join sem_wait or pthread_cond wait. */ + + if (THREAD_GETMEM(self, p_woken_by_cancel) + && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { + THREAD_SETMEM(self, p_woken_by_cancel, 0); pthread_mutex_lock(mutex); - return ETIMEDOUT; + pthread_exit(PTHREAD_CANCELED); } - /* Otherwise, return normally */ + pthread_mutex_lock(mutex); return 0; } @@ -144,7 +374,9 @@ int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, reltime.tv_sec -= 1; } if (reltime.tv_sec < 0) return ETIMEDOUT; - return pthread_cond_timedwait_relative(cond, mutex, &reltime); + + /* Indirect call through pointer! */ + return pthread_cond_tw_rel(cond, mutex, &reltime); } int pthread_cond_signal(pthread_cond_t *cond) diff --git a/linuxthreads/internals.h b/linuxthreads/internals.h index c5fde1f..8af2fca 100644 --- a/linuxthreads/internals.h +++ b/linuxthreads/internals.h @@ -86,6 +86,27 @@ struct pthread_key_struct { typedef struct _pthread_descr_struct * pthread_descr; +/* Callback interface for removing the thread from waiting on an + object if it is cancelled while waiting or about to wait. + This hold a pointer to the object, and a pointer to a function + which ``extricates'' the thread from its enqueued state. + The function takes two arguments: pointer to the wait object, + and a pointer to the thread. It returns 1 if an extrication + actually occured, and hence the thread must also be signalled. + It returns 0 if the thread had already been extricated. */ + +typedef struct _pthread_extricate_struct { + void *pu_object; + int (*pu_extricate_func)(void *, pthread_descr); +} pthread_extricate_if; + +/* Atomic counter made possible by compare_and_swap */ + +struct pthread_atomic { + long p_count; + int p_spinlock; +}; + struct _pthread_descr_struct { pthread_descr p_nextlive, p_prevlive; /* Double chaining of active threads */ @@ -96,6 +117,7 @@ struct _pthread_descr_struct { int p_priority; /* Thread priority (== 0 if not realtime) */ struct _pthread_fastlock * p_lock; /* Spinlock for synchronized accesses */ int p_signal; /* last signal received */ + struct pthread_atomic p_resume_count; /* number of times restart() was called on thread */ sigjmp_buf * p_signal_jmp; /* where to siglongjmp on a signal or NULL */ sigjmp_buf * p_cancel_jmp; /* where to siglongjmp on a cancel or NULL */ char p_terminated; /* true if terminated e.g. by pthread_exit */ @@ -108,6 +130,8 @@ struct _pthread_descr_struct { char p_cancelstate; /* cancellation state */ char p_canceltype; /* cancellation type (deferred/async) */ char p_canceled; /* cancellation request pending */ + char p_woken_by_cancel; /* cancellation performed wakeup */ + pthread_extricate_if *p_extricate; /* See above */ int * p_errnop; /* pointer to used errno variable */ int p_errno; /* error returned by last system call */ int * p_h_errnop; /* pointer to used h_errno variable */ @@ -353,6 +377,7 @@ void __pthread_manager_sighandler(int sig); void __pthread_reset_main_thread(void); void __fresetlockfiles(void); void __pthread_manager_adjust_prio(int thread_prio); +void __pthread_set_own_extricate_if(pthread_descr self, pthread_extricate_if *peif); extern int __pthread_attr_setguardsize (pthread_attr_t *__attr, size_t __guardsize); @@ -372,6 +397,21 @@ extern int __pthread_mutexattr_gettype (const pthread_mutexattr_t *__attr, int *__kind); extern void __pthread_kill_other_threads_np (void); +void __pthread_restart_old(pthread_descr th); +void __pthread_suspend_old(pthread_descr self); + +void __pthread_restart_new(pthread_descr th); +void __pthread_suspend_new(pthread_descr self); + +void __pthread_wait_for_restart_signal(pthread_descr self); + +void __pthread_init_condvar(int rt_sig_available); + +/* Global pointers to old or new suspend functions */ + +extern void (*__pthread_restart)(pthread_descr); +extern void (*__pthread_suspend)(pthread_descr); + /* Prototypes for the function without cancelation support when the normal version has it. */ extern int __libc_close (int fd); diff --git a/linuxthreads/join.c b/linuxthreads/join.c index 71db541..5e6b78a 100644 --- a/linuxthreads/join.c +++ b/linuxthreads/join.c @@ -79,12 +79,37 @@ void pthread_exit(void * retval) _exit(0); } +/* Function called by pthread_cancel to remove the thread from + waiting on a condition variable queue. */ + +static int join_extricate_func(void *obj, pthread_descr th) +{ + volatile pthread_descr self = thread_self(); + pthread_handle handle = obj; + pthread_descr jo; + int did_remove = 0; + + __pthread_lock(&handle->h_lock, self); + jo = handle->h_descr; + did_remove = jo->p_joining != NULL; + jo->p_joining = NULL; + __pthread_unlock(&handle->h_lock); + + return did_remove; +} + int pthread_join(pthread_t thread_id, void ** thread_return) { volatile pthread_descr self = thread_self(); struct pthread_request request; pthread_handle handle = thread_handle(thread_id); pthread_descr th; + pthread_extricate_if extr; + int already_canceled = 0; + + /* Set up extrication interface */ + extr.pu_object = handle; + extr.pu_extricate_func = join_extricate_func; __pthread_lock(&handle->h_lock, self); if (invalid_handle(handle, thread_id)) { @@ -103,13 +128,28 @@ int pthread_join(pthread_t thread_id, void ** thread_return) } /* If not terminated yet, suspend ourselves. */ if (! th->p_terminated) { - th->p_joining = self; + /* Register extrication interface */ + __pthread_set_own_extricate_if(self, &extr); + if (!(THREAD_GETMEM(self, p_canceled) + && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) + th->p_joining = self; + else + already_canceled = 1; __pthread_unlock(&handle->h_lock); - suspend_with_cancellation(self); + + if (already_canceled) { + __pthread_set_own_extricate_if(self, 0); + pthread_exit(PTHREAD_CANCELED); + } + + suspend(self); + /* Deregister extrication interface */ + __pthread_set_own_extricate_if(self, 0); + /* This is a cancellation point */ - if (THREAD_GETMEM(self, p_canceled) + if (THREAD_GETMEM(self, p_woken_by_cancel) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { - th->p_joining = NULL; + THREAD_SETMEM(self, p_woken_by_cancel, 0); pthread_exit(PTHREAD_CANCELED); } __pthread_lock(&handle->h_lock, self); diff --git a/linuxthreads/oldsemaphore.c b/linuxthreads/oldsemaphore.c index 72d12d2..62d2812 100644 --- a/linuxthreads/oldsemaphore.c +++ b/linuxthreads/oldsemaphore.c @@ -68,13 +68,29 @@ int __old_sem_init(old_sem_t *sem, int pshared, unsigned int value) return 0; } +/* Function called by pthread_cancel to remove the thread from + waiting inside __old_sem_wait. Here we simply unconditionally + indicate that the thread is to be woken, by returning 1. */ + +static int old_sem_extricate_func(void *obj, pthread_descr th) +{ + return 1; +} + int __old_sem_wait(old_sem_t * sem) { long oldstatus, newstatus; volatile pthread_descr self = thread_self(); pthread_descr * th; + pthread_extricate_if extr; + + /* Set up extrication interface */ + extr.pu_object = 0; + extr.pu_extricate_func = old_sem_extricate_func; while (1) { + /* Register extrication interface */ + __pthread_set_own_extricate_if(self, &extr); do { oldstatus = sem->sem_status; if ((oldstatus & 1) && (oldstatus != 1)) @@ -85,11 +101,15 @@ int __old_sem_wait(old_sem_t * sem) } } while (! sem_compare_and_swap(sem, oldstatus, newstatus)); - if (newstatus & 1) + if (newstatus & 1) { /* We got the semaphore. */ + __pthread_set_own_extricate_if(self, 0); return 0; + } /* Wait for sem_post or cancellation */ - suspend_with_cancellation(self); + suspend(self); + __pthread_set_own_extricate_if(self, 0); + /* This is a cancellation point */ if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) { /* Remove ourselves from the waiting list if we're still on it */ diff --git a/linuxthreads/pthread.c b/linuxthreads/pthread.c index dfde08f..f082e954 100644 --- a/linuxthreads/pthread.c +++ b/linuxthreads/pthread.c @@ -43,6 +43,7 @@ struct _pthread_descr_struct __pthread_initial_thread = { 0, /* int p_priority */ &__pthread_handles[0].h_lock, /* struct _pthread_fastlock * p_lock */ 0, /* int p_signal */ + ATOMIC_INITIALIZER, /* struct pthread_atomic p_resume_count */ NULL, /* sigjmp_buf * p_signal_buf */ NULL, /* sigjmp_buf * p_cancel_buf */ 0, /* char p_terminated */ @@ -55,6 +56,8 @@ struct _pthread_descr_struct __pthread_initial_thread = { 0, /* char p_cancelstate */ 0, /* char p_canceltype */ 0, /* char p_canceled */ + 0, /* char p_woken_by_cancel */ + NULL, /* struct pthread_extricate_if *p_extricate */ NULL, /* int *p_errnop */ 0, /* int p_errno */ NULL, /* int *p_h_errnop */ @@ -86,6 +89,7 @@ struct _pthread_descr_struct __pthread_manager_thread = { 0, /* int p_priority */ &__pthread_handles[1].h_lock, /* struct _pthread_fastlock * p_lock */ 0, /* int p_signal */ + ATOMIC_INITIALIZER, /* struct pthread_atomic p_resume_count */ NULL, /* sigjmp_buf * p_signal_buf */ NULL, /* sigjmp_buf * p_cancel_buf */ 0, /* char p_terminated */ @@ -98,6 +102,8 @@ struct _pthread_descr_struct __pthread_manager_thread = { 0, /* char p_cancelstate */ 0, /* char p_canceltype */ 0, /* char p_canceled */ + 0, /* char p_woken_by_cancel */ + NULL, /* struct pthread_extricate_if *p_extricate */ &__pthread_manager_thread.p_errno, /* int *p_errnop */ 0, /* int p_errno */ NULL, /* int *p_h_errnop */ @@ -144,6 +150,12 @@ char *__pthread_manager_thread_tos = NULL; int __pthread_exit_requested = 0; int __pthread_exit_code = 0; +/* Pointers that select new or old suspend/resume functions + based on availability of rt signals. */ + +void (*__pthread_restart)(pthread_descr) = __pthread_restart_old; +void (*__pthread_suspend)(pthread_descr) = __pthread_suspend_old; + /* Communicate relevant LinuxThreads constants to gdb */ const int __pthread_threads_max = PTHREAD_THREADS_MAX; @@ -215,13 +227,18 @@ init_rtsigs (void) __pthread_sig_cancel = SIGUSR2; __pthread_sig_debug = 0; #endif + __pthread_init_condvar(0); } else { #if __SIGRTMAX - __SIGRTMIN >= 3 current_rtmin = __SIGRTMIN + 3; + __pthread_restart = __pthread_restart_new; + __pthread_suspend = __pthread_wait_for_restart_signal; + __pthread_init_condvar(1); #else current_rtmin = __SIGRTMIN; + __pthread_init_condvar(0); #endif current_rtmax = __SIGRTMAX; @@ -447,7 +464,7 @@ int __pthread_initialize_manager(void) raise(__pthread_sig_debug); /* We suspend ourself and gdb will wake us up when it is ready to handle us. */ - suspend(thread_self()); + __pthread_wait_for_restart_signal(thread_self()); } /* Synchronize debugging of the thread manager */ request.req_kind = REQ_DEBUG; @@ -770,6 +787,53 @@ int __pthread_getconcurrency(void) } weak_alias (__pthread_getconcurrency, pthread_getconcurrency) +void __pthread_set_own_extricate_if(pthread_descr self, pthread_extricate_if *peif) +{ + __pthread_lock(self->p_lock, self); + THREAD_SETMEM(self, p_extricate, peif); + __pthread_unlock(self->p_lock); +} + +/* Primitives for controlling thread execution */ + +void __pthread_wait_for_restart_signal(pthread_descr self) +{ + sigset_t mask; + + sigprocmask(SIG_SETMASK, NULL, &mask); /* Get current signal mask */ + sigdelset(&mask, __pthread_sig_restart); /* Unblock the restart signal */ + do { + self->p_signal = 0; + sigsuspend(&mask); /* Wait for signal */ + } while (self->p_signal !=__pthread_sig_restart ); +} + +/* The _old variants are for 2.0 and early 2.1 kernels which don't have RT signals. + On these kernels, we use SIGUSR1 and SIGUSR2 for restart and cancellation. + Since the restart signal does not queue, we use an atomic counter to create + queuing semantics. This is needed to resolve a rare race condition in + pthread_cond_timedwait_relative. */ + +void __pthread_restart_old(pthread_descr th) +{ + if (atomic_increment(&th->p_resume_count) == -1) + kill(th->p_pid, __pthread_sig_restart); +} + +void __pthread_suspend_old(pthread_descr self) +{ + if (atomic_decrement(&self->p_resume_count) <= 0) + __pthread_wait_for_restart_signal(self); +} + +void __pthread_restart_new(pthread_descr th) +{ + kill(th->p_pid, __pthread_sig_restart); +} + +/* There is no __pthread_suspend_new because it would just + be a wasteful wrapper for __pthread_wait_for_restart_signal */ + /* Debugging aid */ #ifdef DEBUG diff --git a/linuxthreads/queue.h b/linuxthreads/queue.h index fa8c5d8..f87322f 100644 --- a/linuxthreads/queue.h +++ b/linuxthreads/queue.h @@ -43,13 +43,14 @@ static inline pthread_descr dequeue(pthread_descr * q) return th; } -static inline void remove_from_queue(pthread_descr * q, pthread_descr th) +static inline int remove_from_queue(pthread_descr * q, pthread_descr th) { for (; *q != NULL; q = &((*q)->p_nextwaiting)) { if (*q == th) { *q = th->p_nextwaiting; th->p_nextwaiting = NULL; - return; + return 1; } } + return 0; } diff --git a/linuxthreads/restart.h b/linuxthreads/restart.h index 7492013..702d7d1 100644 --- a/linuxthreads/restart.h +++ b/linuxthreads/restart.h @@ -18,41 +18,10 @@ static inline void restart(pthread_descr th) { - kill(th->p_pid, __pthread_sig_restart); + __pthread_restart(th); /* see pthread.c */ } static inline void suspend(pthread_descr self) { - sigset_t mask; - - sigprocmask(SIG_SETMASK, NULL, &mask); /* Get current signal mask */ - sigdelset(&mask, __pthread_sig_restart); /* Unblock the restart signal */ - do { - self->p_signal = 0; - sigsuspend(&mask); /* Wait for signal */ - } while (self->p_signal !=__pthread_sig_restart ); -} - -#define suspend_with_cancellation(self) \ -{ \ - sigset_t mask; \ - sigjmp_buf jmpbuf; \ - \ - sigprocmask(SIG_SETMASK, NULL, &mask); /* Get current signal mask */ \ - sigdelset(&mask, __pthread_sig_restart); /* Unblock the restart signal */ \ - /* No need to save the signal mask, we'll restore it ourselves */ \ - if (sigsetjmp(jmpbuf, 0) == 0) { \ - self->p_cancel_jmp = &jmpbuf; \ - if (! (self->p_canceled \ - && self->p_cancelstate == PTHREAD_CANCEL_ENABLE)) { \ - do { \ - self->p_signal = 0; \ - sigsuspend(&mask); /* Wait for a signal */ \ - } while (self->p_signal != __pthread_sig_restart); \ - } \ - self->p_cancel_jmp = NULL; \ - } else { \ - sigaddset(&mask, __pthread_sig_restart); /* Reblock the restart signal */ \ - sigprocmask(SIG_SETMASK, &mask, NULL); \ - } \ + __pthread_suspend(self); /* see pthread.c */ } diff --git a/linuxthreads/rwlock.c b/linuxthreads/rwlock.c index 1fb18a3..1d78b78 100644 --- a/linuxthreads/rwlock.c +++ b/linuxthreads/rwlock.c @@ -23,8 +23,8 @@ #include <pthread.h> #include "internals.h" #include "queue.h" -#include "restart.h" #include "spinlock.h" +#include "restart.h" int pthread_rwlock_init (pthread_rwlock_t *rwlock, diff --git a/linuxthreads/semaphore.c b/linuxthreads/semaphore.c index cfad97a..0297b3a 100644 --- a/linuxthreads/semaphore.c +++ b/linuxthreads/semaphore.c @@ -38,9 +38,31 @@ int __new_sem_init(sem_t *sem, int pshared, unsigned int value) return 0; } +/* Function called by pthread_cancel to remove the thread from + waiting inside __new_sem_wait. */ + +static int new_sem_extricate_func(void *obj, pthread_descr th) +{ + volatile pthread_descr self = thread_self(); + sem_t *sem = obj; + int did_remove = 0; + + __pthread_lock((struct _pthread_fastlock *) &sem->__sem_lock, self); + did_remove = remove_from_queue(&sem->__sem_waiting, th); + __pthread_unlock((struct _pthread_fastlock *) &sem->__sem_lock); + + return did_remove; +} + int __new_sem_wait(sem_t * sem) { volatile pthread_descr self = thread_self(); + pthread_extricate_if extr; + int already_canceled = 0; + + /* Set up extrication interface */ + extr.pu_object = sem; + extr.pu_extricate_func = new_sem_extricate_func; __pthread_lock((struct _pthread_fastlock *) &sem->__sem_lock, self); if (sem->__sem_value > 0) { @@ -48,17 +70,31 @@ int __new_sem_wait(sem_t * sem) __pthread_unlock((struct _pthread_fastlock *) &sem->__sem_lock); return 0; } - enqueue(&sem->__sem_waiting, self); - /* Wait for sem_post or cancellation */ + /* Register extrication interface */ + __pthread_set_own_extricate_if(self, &extr); + /* Enqueue only if not already cancelled. */ + if (!(THREAD_GETMEM(self, p_canceled) + && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) + enqueue(&sem->__sem_waiting, self); + else + already_canceled = 1; __pthread_unlock((struct _pthread_fastlock *) &sem->__sem_lock); - suspend_with_cancellation(self); - /* This is a cancellation point */ - if (THREAD_GETMEM(self, p_canceled) + + if (already_canceled) { + __pthread_set_own_extricate_if(self, 0); + pthread_exit(PTHREAD_CANCELED); + } + + /* Wait for sem_post or cancellation, or fall through if already canceled */ + suspend(self); + __pthread_set_own_extricate_if(self, 0); + + /* Terminate only if the wakeup came from cancellation. */ + /* Otherwise ignore cancellation because we got the semaphore. */ + + if (THREAD_GETMEM(self, p_woken_by_cancel) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { - /* Remove ourselves from the waiting list if we're still on it */ - __pthread_lock((struct _pthread_fastlock *) &sem->__sem_lock, self); - remove_from_queue(&sem->__sem_waiting, self); - __pthread_unlock((struct _pthread_fastlock *) &sem->__sem_lock); + THREAD_SETMEM(self, p_woken_by_cancel, 0); pthread_exit(PTHREAD_CANCELED); } /* We got the semaphore */ diff --git a/linuxthreads/spinlock.c b/linuxthreads/spinlock.c index ce6ff9e..b1a99d9 100644 --- a/linuxthreads/spinlock.c +++ b/linuxthreads/spinlock.c @@ -40,6 +40,7 @@ void internal_function __pthread_lock(struct _pthread_fastlock * lock, pthread_descr self) { long oldstatus, newstatus; + int spurious_wakeup_count = 0; do { oldstatus = lock->__status; @@ -56,7 +57,28 @@ void internal_function __pthread_lock(struct _pthread_fastlock * lock, } } while(! compare_and_swap(&lock->__status, oldstatus, newstatus, &lock->__spinlock)); - if (oldstatus != 0) suspend(self); + + /* Suspend with guard against spurious wakeup. + This can happen in pthread_cond_timedwait_relative, when the thread + wakes up due to timeout and is still on the condvar queue, and then + locks the queue to remove itself. At that point it may still be on the + queue, and may be resumed by a condition signal. */ + + if (oldstatus != 0) { + for (;;) { + suspend(self); + if (self->p_nextlock != NULL) { + /* Count resumes that don't belong to us. */ + spurious_wakeup_count++; + continue; + } + break; + } + } + + /* Put back any resumes we caught that don't belong to us. */ + while (spurious_wakeup_count--) + restart(self); } void internal_function __pthread_unlock(struct _pthread_fastlock * lock) diff --git a/linuxthreads/spinlock.h b/linuxthreads/spinlock.h index 29f0304..aae18a2 100644 --- a/linuxthreads/spinlock.h +++ b/linuxthreads/spinlock.h @@ -72,3 +72,31 @@ static inline int __pthread_trylock (struct _pthread_fastlock * lock) } #define LOCK_INITIALIZER {0, 0} + +/* Operations on pthread_atomic, which is defined in internals.h */ + +static inline long atomic_increment(struct pthread_atomic *pa) +{ + long oldval; + + do { + oldval = pa->p_count; + } while (!compare_and_swap(&pa->p_count, oldval, oldval + 1, &pa->p_spinlock)); + + return oldval; +} + + +static inline long atomic_decrement(struct pthread_atomic *pa) +{ + long oldval; + + do { + oldval = pa->p_count; + } while (!compare_and_swap(&pa->p_count, oldval, oldval - 1, &pa->p_spinlock)); + + return oldval; +} + +#define ATOMIC_INITIALIZER { 0, 0 } + |