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| | #include "pthread_impl.h"
#include <semaphore.h>
#include <string.h>
static void dummy_0(void)
{
}
weak_alias(dummy_0, __tl_lock);
weak_alias(dummy_0, __tl_unlock);
static int target_tid;
static void (*callback)(void *), *context;
static sem_t target_sem, caller_sem;
static void dummy(void *p)
{
}
static void handler(int sig)
{
if (__pthread_self()->tid != target_tid) return;
int old_errno = errno;
/* Inform caller we have received signal and wait for
* the caller to let us make the callback. */
sem_post(&caller_sem);
sem_wait(&target_sem);
callback(context);
/* Inform caller we've complered the callback and wait
* for the caller to release us to return. */
sem_post(&caller_sem);
sem_wait(&target_sem);
/* Inform caller we are returning and state is destroyable. */
sem_post(&caller_sem);
errno = old_errno;
}
void __synccall(void (*func)(void *), void *ctx)
{
sigset_t oldmask;
int cs, i, r;
struct sigaction sa = { .sa_flags = SA_RESTART, .sa_handler = handler };
pthread_t self = __pthread_self(), td;
int count = 0;
/* Blocking signals in two steps, first only app-level signals
* before taking the lock, then all signals after taking the lock,
* is necessary to achieve AS-safety. Blocking them all first would
* deadlock if multiple threads called __synccall. Waiting to block
* any until after the lock would allow re-entry in the same thread
* with the lock already held. */
__block_app_sigs(&oldmask);
__tl_lock();
__block_all_sigs(0);
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
sem_init(&target_sem, 0, 0);
sem_init(&caller_sem, 0, 0);
if (!libc.threads_minus_1) goto single_threaded;
callback = func;
context = ctx;
/* Block even implementation-internal signals, so that nothing
* interrupts the SIGSYNCCALL handlers. The main possible source
* of trouble is asynchronous cancellation. */
memset(&sa.sa_mask, -1, sizeof sa.sa_mask);
__libc_sigaction(SIGSYNCCALL, &sa, 0);
for (td=self->next; td!=self; td=td->next) {
target_tid = td->tid;
while ((r = -__syscall(SYS_tkill, td->tid, SIGSYNCCALL)) == EAGAIN);
if (r) {
/* If we failed to signal any thread, nop out the
* callback to abort the synccall and just release
* any threads already caught. */
callback = func = dummy;
break;
}
sem_wait(&caller_sem);
count++;
}
target_tid = 0;
/* Serialize execution of callback in caught threads, or just
* release them all if synccall is being aborted. */
for (i=0; i<count; i++) {
sem_post(&target_sem);
sem_wait(&caller_sem);
}
sa.sa_handler = SIG_IGN;
__libc_sigaction(SIGSYNCCALL, &sa, 0);
single_threaded:
func(ctx);
/* Only release the caught threads once all threads, including the
* caller, have returned from the callback function. */
for (i=0; i<count; i++)
sem_post(&target_sem);
for (i=0; i<count; i++)
sem_wait(&caller_sem);
sem_destroy(&caller_sem);
sem_destroy(&target_sem);
pthread_setcancelstate(cs, 0);
__tl_unlock();
__restore_sigs(&oldmask);
}
|