Implement condition variables (POSIX only!)

Windows requires Vista or newer to get the CONDITION_VARIABNLE API, but we
currently only require XP.

common/threads.c

@@ -170,7 +170,8 @@ int althrd_join(althrd_t thr, int *res)
     GetExitCodeThread(hdl, &code);
     CloseHandle(hdl);
 
-    *res = (int)code;
+    if(res != NULL)
+        *res = (int)code;
     return althrd_success;
 }
 
@@ -412,11 +413,10 @@ int althrd_join(althrd_t thr, int *res)
 {
     void *code;
 
-    if(!res) return althrd_error;
-
     if(pthread_join(thr, &code) != 0)
         return althrd_error;
-    *res = (int)(intptr_t)code;
+    if(res != NULL)
+        *res = (int)(intptr_t)code;
     return althrd_success;
 }
 
@@ -495,6 +495,46 @@ int almtx_timedlock(almtx_t *mtx, const struct timespec *ts)
 #endif
 }
 
+int alcnd_init(alcnd_t *cond)
+{
+    if(pthread_cond_init(cond, NULL) == 0)
+        return althrd_success;
+    return althrd_error;
+}
+
+int alcnd_signal(alcnd_t *cond)
+{
+    if(pthread_cond_signal(cond) == 0)
+        return althrd_success;
+    return althrd_error;
+}
+
+int alcnd_broadcast(alcnd_t *cond)
+{
+    if(pthread_cond_broadcast(cond) == 0)
+        return althrd_success;
+    return althrd_error;
+}
+
+int alcnd_wait(alcnd_t *cond, almtx_t *mtx)
+{
+    if(pthread_cond_wait(cond, mtx) == 0)
+        return althrd_success;
+    return althrd_error;
+}
+
+int alcnd_timedwait(alcnd_t *cond, almtx_t *mtx, const struct timespec *time_point)
+{
+    if(pthread_cond_timedwait(cond, mtx, time_point) == 0)
+        return althrd_success;
+    return althrd_error;
+}
+
+void alcnd_destroy(alcnd_t *cond)
+{
+    pthread_cond_destroy(cond);
+}
+
 
 int altss_create(altss_t *tss_id, altss_dtor_t callback)
 {

include/threads.h

@@ -113,12 +113,23 @@ inline int altss_set(altss_t tss_id, void *val)
 
 typedef pthread_t althrd_t;
 typedef pthread_mutex_t almtx_t;
+typedef pthread_cond_t alcnd_t;
 typedef pthread_key_t altss_t;
 typedef pthread_once_t alonce_flag;
 
 #define AL_ONCE_FLAG_INIT PTHREAD_ONCE_INIT
 
 
+/* NOTE: Condition variables are POSIX-only at the moment, as Windows requires
+ * Vista or newer for them (without slow, hacky work-arounds). */
+int alcnd_init(alcnd_t *cond);
+int alcnd_signal(alcnd_t *cond);
+int alcnd_broadcast(alcnd_t *cond);
+int alcnd_wait(alcnd_t *cond, almtx_t *mtx);
+int alcnd_timedwait(alcnd_t *cond, almtx_t *mtx, const struct timespec *time_point);
+void alcnd_destroy(alcnd_t *cond);
+
+
 inline althrd_t althrd_current(void)
 {
     return pthread_self();