simplify barrier to use only a mutex and condition variable

cxx/include/rt/barrier.hpp

@@ -8,7 +8,7 @@ namespace rt
 class barrier
 {
   public:
-    constexpr barrier(int count) : b(RT_BARRIER_INIT(b, count))
+    constexpr barrier(unsigned int count) : b(RT_BARRIER_INIT(b, count))
     {
     }
 

include/rt/barrier.h

@@ -3,7 +3,6 @@
 
 #include <rt/cond.h>
 #include <rt/mutex.h>
-#include <rt/sem.h>
 
 #include <stdbool.h>
 
@@ -13,7 +12,7 @@ extern "C" {
 
 struct rt_barrier;
 
-void rt_barrier_init(struct rt_barrier *barrier, int count);
+void rt_barrier_init(struct rt_barrier *barrier, unsigned int count);
 
 /*
  * Blocks until count threads have called it, at which point it returns
@@ -24,17 +23,15 @@ bool rt_barrier_wait(struct rt_barrier *barrier);
 
 struct rt_barrier
 {
-    struct rt_sem sem;
     struct rt_mutex mutex;
     struct rt_cond cond;
-    int level, threshold;
+    unsigned int level, threshold, generation;
 };
 
 #define RT_BARRIER_INIT(name, count)                                           \
     {                                                                          \
-        .sem = RT_SEM_INIT(name.sem, count),                                   \
         .mutex = RT_MUTEX_INIT(name.mutex), .cond = RT_COND_INIT(name.cond),   \
-        .level = 0, .threshold = (count),                                      \
+        .level = 0, .threshold = (count), .generation = 0,                     \
     }
 
 #define RT_BARRIER(name, count)                                                \

src/barrier.c

@@ -1,35 +1,33 @@
 #include <rt/barrier.h>
 
-void rt_barrier_init(struct rt_barrier *barrier, int count)
+void rt_barrier_init(struct rt_barrier *barrier, unsigned int count)
 {
-    barrier->level = 0;
-    barrier->threshold = count;
-    rt_sem_init(&barrier->sem, count);
     rt_mutex_init(&barrier->mutex);
     rt_cond_init(&barrier->cond);
+    barrier->level = 0;
+    barrier->threshold = count;
+    barrier->generation = 0;
 }
 
 bool rt_barrier_wait(struct rt_barrier *barrier)
 {
-    rt_sem_wait(&barrier->sem);
-
     rt_mutex_lock(&barrier->mutex);
+    const unsigned int generation = barrier->generation;
     ++barrier->level;
-    if (barrier->level == barrier->threshold)
+    const bool is_leader = barrier->level == barrier->threshold;
+    if (is_leader)
     {
+        barrier->level = 0;
+        ++barrier->generation;
         rt_cond_broadcast(&barrier->cond);
     }
     else
     {
-        rt_cond_wait(&barrier->cond, &barrier->mutex);
-    }
-    --barrier->level;
-    const bool complete = barrier->level == 0;
-    if (complete)
-    {
-        rt_sem_post_n(&barrier->sem, barrier->threshold);
+        while (generation == barrier->generation)
+        {
+            rt_cond_wait(&barrier->cond, &barrier->mutex);
+        }
     }
     rt_mutex_unlock(&barrier->mutex);
-
-    return complete;
+    return is_leader;
 }