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12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455#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;}