AP_HAL_Empty: implement new Semaphore interface

libraries/AP_HAL_Empty/Semaphores.cpp

@@ -3,38 +3,25 @@
 
 using namespace Empty;
 
-EmptySemaphore::EmptySemaphore() :
-    _owner(NULL),
-    _k(NULL)
-{}
-
-
-bool EmptySemaphore::get(void* owner) {
-    if (_owner == NULL) {
-        _owner = owner;
+bool EmptySemaphore::give() {
+    if (_taken) {
+        _taken = false;
         return true;
     } else {
         return false;
     }
 }
 
-bool EmptySemaphore::release(void* owner) {
-    if (_owner == NULL || _owner != owner) {
-        return false;
-    } else {
-        _owner = NULL;
-        if (_k){
-            _k();
-            _k = NULL;
-        }
-        return true;
-    }
+bool EmptySemaphore::take(uint32_t timeout_ms) {
+    return take_nonblocking();
 }
 
-bool EmptySemaphore::call_on_release(void* caller, AP_HAL::Proc k) {
-    /* idk what semantics randy was looking for here, honestly.
-     * seems like a bad idea. */
-    _k = k;
-    return true;
+bool EmptySemaphore::take_nonblocking() {
+    /* No syncronisation primitives to garuntee this is correct */
+    if (!_taken) {
+        _taken = true;
+        return true;
+    } else {
+        return false;
+    }
 }
-

libraries/AP_HAL_Empty/Semaphores.h

@@ -6,17 +6,12 @@
 
 class Empty::EmptySemaphore : public AP_HAL::Semaphore {
 public:
-    EmptySemaphore();
-    // get - to claim ownership of the semaphore
-    bool get(void* owner);
-    // release - to give up ownership of the semaphore
-    bool release(void* owner);
-    // call_on_release - returns true if caller successfully added to the
-    // queue to be called back
-    bool call_on_release(void* caller, AP_HAL::Proc k);
+    EmptySemaphore() : _taken(false) {}
+    bool give();
+    bool take(uint32_t timeout_ms);
+    bool take_nonblocking();
 private:
-    void* _owner;
-    AP_HAL::Proc _k;
+    bool _taken;
 };
 
 #endif // __AP_HAL_EMPTY_SEMAPHORE_H__