diff options
| -rw-r--r-- | misc/rendezvous.c | 54 | ||||
| -rw-r--r-- | misc/rendezvous.h | 8 | ||||
| -rw-r--r-- | old-makefile | 1 | ||||
| -rw-r--r-- | wscript_build.py | 1 |
4 files changed, 64 insertions, 0 deletions
diff --git a/misc/rendezvous.c b/misc/rendezvous.c new file mode 100644 index 0000000000..9af798dd07 --- /dev/null +++ b/misc/rendezvous.c @@ -0,0 +1,54 @@ +#include <pthread.h> + +#include "rendezvous.h" + +static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER; +static pthread_cond_t wakeup = PTHREAD_COND_INITIALIZER; + +static struct waiter *waiters; + +struct waiter { + void *tag; + struct waiter *next; + intptr_t *value; +}; + +/* A barrier for 2 threads, which can exchange a value when they meet. + * The first thread to call this function will block. As soon as two threads + * are calling this function with the same tag value, they will unblock, and + * on each thread the call return the value parameter of the _other_ thread. + * + * tag is an arbitrary value, but it must be an unique pointer. If there are + * more than 2 threads using the same tag, things won't work. Typically, it + * will have to point to a memory allocation or to the stack, while pointing + * it to static data is always a bug. + * + * This shouldn't be used for performance critical code (uses a linked list + * of _all_ waiters in the process, and temporarily wakes up _all_ waiters on + * each second call). + * + * This is inspired by: http://9atom.org/magic/man2html/2/rendezvous */ +intptr_t mp_rendezvous(void *tag, intptr_t value) +{ + struct waiter wait = { .tag = tag, .value = &value }; + pthread_mutex_lock(&lock); + struct waiter **prev = &waiters; + while (*prev) { + if ((*prev)->tag == tag) { + intptr_t tmp = *(*prev)->value; + *(*prev)->value = value; + value = tmp; + (*prev)->value = NULL; // signals completion + *prev = (*prev)->next; // unlink + pthread_cond_broadcast(&wakeup); + goto done; + } + prev = &(*prev)->next; + } + *prev = &wait; + while (wait.value) + pthread_cond_wait(&wakeup, &lock); +done: + pthread_mutex_unlock(&lock); + return value; +} diff --git a/misc/rendezvous.h b/misc/rendezvous.h new file mode 100644 index 0000000000..ffcc89a22c --- /dev/null +++ b/misc/rendezvous.h @@ -0,0 +1,8 @@ +#ifndef MP_RENDEZVOUS_H_ +#define MP_RENDEZVOUS_H_ + +#include <stdint.h> + +intptr_t mp_rendezvous(void *tag, intptr_t value); + +#endif diff --git a/old-makefile b/old-makefile index c5d8e6a223..a1d98e60ec 100644 --- a/old-makefile +++ b/old-makefile @@ -177,6 +177,7 @@ SOURCES = audio/audio.c \ input/keycodes.c \ misc/charset_conv.c \ misc/dispatch.c \ + misc/rendezvous.c \ misc/ring.c \ options/m_config.c \ options/m_option.c \ diff --git a/wscript_build.py b/wscript_build.py index 62446d1907..463c3c1084 100644 --- a/wscript_build.py +++ b/wscript_build.py @@ -201,6 +201,7 @@ def build(ctx): ( "misc/charset_conv.c" ), ( "misc/dispatch.c" ), ( "misc/ring.c" ), + ( "misc/rendezvous.c" ), ## Options ( "options/m_config.c" ), |