POSIX: Add sem_getvalue() abstraction

src/platforms/posix/px4_layer/px4_sem.cpp

@@ -85,6 +85,16 @@ int px4_sem_post(px4_sem_t *s)
 	return 0;
 }
 
+int px4_sem_getvalue(px4_sem_t *s)
+{
+	int val;
+	pthread_mutex_lock(&(s->lock));
+	val = s->value;
+	pthread_mutex_unlock(&(s->lock));
+
+	return val;
+}
+
 int px4_sem_destroy(px4_sem_t *s)
 {
 	pthread_mutex_lock(&(s->lock));

src/platforms/px4_posix.h

@@ -64,6 +64,7 @@ typedef struct
 __EXPORT int		px4_sem_init(px4_sem_t *s, int pshared, unsigned value);
 __EXPORT int		px4_sem_wait(px4_sem_t *s);
 __EXPORT int		px4_sem_post(px4_sem_t *s);
+__EXPORT int		px4_sem_getvalue(px4_sem_t *s);
 __EXPORT int		px4_sem_destroy(px4_sem_t *s);
 
 __END_DECLS
@@ -75,6 +76,7 @@ typedef px4_sem_t		sem_t
 #define px4_sem_init		_GLOBAL sem_init
 #define px4_sem_wait		_GLOBAL sem_wait
 #define px4_sem_post		_GLOBAL px4_sem_post
+#define px4_sem_getvalue	_GLOBAL px4_sem_getvalue
 #define px4_sem_destroy		_GLOBAL sem_destroy