Adopted posix semaphore in posix implementation

Using sem_t over posix_cond_t is a simpler implementation
of events_sema_t. The only downside is that sem_t does not
have a binary version.

Makefile

@@ -20,7 +20,7 @@ endif
 CFLAGS += -I.
 CFLAGS += -std=c99
 CFLAGS += -Wall
-CFLAGS += -D_XOPEN_SOURCE=500
+CFLAGS += -D_XOPEN_SOURCE=600
 
 LFLAGS += -lpthread
 

events_posix.c

@@ -40,46 +40,30 @@ void events_mutex_unlock(events_mutex_t *m) {
 }
 
 
+// Semaphore operations
 int events_sema_create(events_sema_t *s) {
-    int err = pthread_mutex_init(&s->mutex, 0);
-    if (err) {
-        return err;
-    }
-
-    err = pthread_cond_init(&s->cond, 0);
-    if (err) {
-        return err;
-    }
-
-    return 0;
+    return sem_init(s, 0, 0);
 }
 
 void events_sema_destroy(events_sema_t *s) {
-    pthread_mutex_destroy(&s->mutex);
-    pthread_cond_destroy(&s->cond);
+    sem_destroy(s);
 }
 
 void events_sema_release(events_sema_t *s) {
-    pthread_cond_signal(&s->cond);
+    sem_post(s);
 }
 
 bool events_sema_wait(events_sema_t *s, int ms) {
-    int err;
-    pthread_mutex_lock(&s->mutex);
-
     if (ms < 0) {
-        err = pthread_cond_wait(&s->cond, &s->mutex);
+        return !sem_wait(s);
     } else {
         ms += events_tick();
         struct timespec ts = {
             .tv_sec = ms/1000,
             .tv_nsec = ms*1000000,
         };
-        err = pthread_cond_timedwait(&s->cond, &s->mutex, &ts);
+        return !sem_timedwait(s, &ts);
     }
-
-    pthread_mutex_unlock(&s->mutex);
-    return !err;
 }
 
 #endif

events_sema.h

@@ -19,11 +19,8 @@ extern "C" {
 // Optimal implementation is a binary semaphore,
 // however a regular semaphore is sufficient.
 #if defined(__unix__)
-#include <pthread.h>
-typedef struct {
-    pthread_mutex_t mutex;
-    pthread_cond_t cond;
-} events_sema_t;
+#include <semaphore.h>
+typedef sem_t events_sema_t;
 #elif defined(__MBED__)
 #ifdef MBED_CONF_RTOS_PRESENT
 typedef void *events_sema_t;