HAL_PX4: added Semaphore_Recursive

libraries/AP_HAL_PX4/AP_HAL_PX4_Namespace.h

@@ -15,6 +15,7 @@ namespace PX4 {
     class PX4I2CDriver;
     class PX4_I2C;
     class Semaphore;
+    class Semaphore_Recursive;
     class PX4CAN;
     class PX4CANManager;
 }

libraries/AP_HAL_PX4/Semaphores.cpp

@@ -9,6 +9,21 @@ extern const AP_HAL::HAL& hal;
 
 using namespace PX4;
 
+// construct a semaphore
+Semaphore::Semaphore()
+{
+    pthread_mutex_init(&_lock, nullptr);
+}
+
+// construct a recursive semaphore (allows a thread to take it more than once)
+Semaphore_Recursive::Semaphore_Recursive()
+{
+    pthread_mutexattr_t attr;
+    pthread_mutexattr_init(&attr);
+    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+    pthread_mutex_init(&_lock, &attr);
+}
+
 bool Semaphore::give() 
 {
     return pthread_mutex_unlock(&_lock) == 0;

libraries/AP_HAL_PX4/Semaphores.h

@@ -9,13 +9,17 @@
 
 class PX4::Semaphore : public AP_HAL::Semaphore {
 public:
-    Semaphore() {
-        pthread_mutex_init(&_lock, nullptr);
-    }
+    Semaphore();
     bool give();
     bool take(uint32_t timeout_ms);
     bool take_nonblocking();
-private:
+protected:
     pthread_mutex_t _lock;
 };
 
+class PX4::Semaphore_Recursive : public PX4::Semaphore {
+public:
+    Semaphore_Recursive();
+};
+
+