1 #include "pthread_impl.h"
5 static void dummy_0(void)
9 weak_alias(dummy_0, __tl_lock);
10 weak_alias(dummy_0, __tl_unlock);
12 static int target_tid;
13 static void (*callback)(void *), *context;
14 static sem_t target_sem, caller_sem;
16 static void dummy(void *p)
20 static void handler(int sig)
22 if (__pthread_self()->tid != target_tid) return;
24 int old_errno = errno;
26 /* Inform caller we have received signal and wait for
27 * the caller to let us make the callback. */
28 sem_post(&caller_sem);
29 sem_wait(&target_sem);
33 /* Inform caller we've complered the callback and wait
34 * for the caller to release us to return. */
35 sem_post(&caller_sem);
36 sem_wait(&target_sem);
38 /* Inform caller we are returning and state is destroyable. */
39 sem_post(&caller_sem);
44 void __synccall(void (*func)(void *), void *ctx)
48 struct sigaction sa = { .sa_flags = SA_RESTART, .sa_handler = handler };
49 pthread_t self = __pthread_self(), td;
52 /* Blocking signals in two steps, first only app-level signals
53 * before taking the lock, then all signals after taking the lock,
54 * is necessary to achieve AS-safety. Blocking them all first would
55 * deadlock if multiple threads called __synccall. Waiting to block
56 * any until after the lock would allow re-entry in the same thread
57 * with the lock already held. */
58 __block_app_sigs(&oldmask);
61 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
63 sem_init(&target_sem, 0, 0);
64 sem_init(&caller_sem, 0, 0);
66 if (!libc.threads_minus_1) goto single_threaded;
71 /* Block even implementation-internal signals, so that nothing
72 * interrupts the SIGSYNCCALL handlers. The main possible source
73 * of trouble is asynchronous cancellation. */
74 memset(&sa.sa_mask, -1, sizeof sa.sa_mask);
75 __libc_sigaction(SIGSYNCCALL, &sa, 0);
78 for (td=self->next; td!=self; td=td->next) {
80 while ((r = -__syscall(SYS_tkill, td->tid, SIGSYNCCALL)) == EAGAIN);
82 /* If we failed to signal any thread, nop out the
83 * callback to abort the synccall and just release
84 * any threads already caught. */
85 callback = func = dummy;
88 sem_wait(&caller_sem);
93 /* Serialize execution of callback in caught threads, or just
94 * release them all if synccall is being aborted. */
95 for (i=0; i<count; i++) {
96 sem_post(&target_sem);
97 sem_wait(&caller_sem);
100 sa.sa_handler = SIG_IGN;
101 __libc_sigaction(SIGSYNCCALL, &sa, 0);
106 /* Only release the caught threads once all threads, including the
107 * caller, have returned from the callback function. */
108 for (i=0; i<count; i++)
109 sem_post(&target_sem);
110 for (i=0; i<count; i++)
111 sem_wait(&caller_sem);
113 sem_destroy(&caller_sem);
114 sem_destroy(&target_sem);
116 pthread_setcancelstate(cs, 0);
118 __restore_sigs(&oldmask);