Replace semaphores with task notifications. (#9)

* Replace all semaphores with task notifications.

* use critical sections to prevent concurrent data access.

* Ensure scan stop has been called before connecting.

* Optimize and cleanup

* Add template casting to NimBLERemoteDescriptor::readValue()

* Removed storage of the descriptor value read as it did not serve any purpose.

src/NimBLERemoteCharacteristic.h

@@ -32,6 +32,12 @@ class NimBLERemoteDescriptor;
 typedef void (*notify_callback)(NimBLERemoteCharacteristic* pBLERemoteCharacteristic,
                                 uint8_t* pData, size_t length, bool isNotify);
 
+typedef struct {
+    const NimBLEUUID *uuid;
+    void *task_data;
+} desc_filter_t;
+
+
 /**
  * @brief A model of a remote %BLE characteristic.
  */
@@ -110,7 +116,6 @@ private:
                                struct ble_gatt_attr *attr, void *arg);
     static int        onWriteCB(uint16_t conn_handle, const struct ble_gatt_error *error,
                                 struct ble_gatt_attr *attr, void *arg);
-    void              releaseSemaphores();
     static int        descriptorDiscCB(uint16_t conn_handle, const struct ble_gatt_error *error,
                                        uint16_t chr_val_handle, const struct ble_gatt_dsc *dsc,
                                        void *arg);
@@ -121,12 +126,10 @@ private:
     uint16_t                m_handle;
     uint16_t                m_defHandle;
     NimBLERemoteService*    m_pRemoteService;
-    FreeRTOS::Semaphore     m_semaphoreGetDescEvt       = FreeRTOS::Semaphore("GetDescEvt");
-    FreeRTOS::Semaphore     m_semaphoreReadCharEvt      = FreeRTOS::Semaphore("ReadCharEvt");
-    FreeRTOS::Semaphore     m_semaphoreWriteCharEvt     = FreeRTOS::Semaphore("WriteCharEvt");
     std::string             m_value;
     notify_callback         m_notifyCallback;
     time_t                  m_timestamp;
+    portMUX_TYPE            m_valMux;
 
     // We maintain a vector of descriptors owned by this characteristic.
     std::vector<NimBLERemoteDescriptor*> m_descriptorVector;