Resolve circular references (p1): C++ GATTHandler, GATTService, pp are not owner of their resepctive backreference

GATTHandler, GATTService, pp are not owner of their resepctive backreference,
hence use std::weak_ptr for backreferences in general and validate on usage (nullptr, if destructed).

No DBTDevice has been ever destructed after using GATTHandler and discovering all GATT services.
In contrast to Java, C++ has no magic GC and hence shared_ptr use_count gets only increased
when emplying circular backreferences - none gets destructed.

Current ownership relationship is:
  DBTAdapter -> DBTDevice -> GATTHandler -> GATTService ...

each contains a backreference, now using a weak_ptr.

Result is that depending on the use-case, DBTDevice instances are destructed:
- Using device->remove(): Immediately
- No explicit device->remove(): Adapter keeps sharedDevices, destruction occurs at end.

1 files changed, 6 insertions, 3 deletions

diff --git a/api/direct_bt/GATTService.hpp b/api/direct_bt/GATTService.hpp
index c02628fe..fd70e24a 100644
--- a/api/direct_bt/GATTService.hpp
+++ b/api/direct_bt/GATTService.hpp
@@ -62,10 +62,11 @@ namespace direct_bt {
      * which also may include its client config if available.
      */
     class GATTService : public JavaUplink {
-        public:
+        private:
             /* Service's Device back-reference */
-            std::shared_ptr<DBTDevice> device;
+            std::weak_ptr<DBTDevice> wbr_device;
 
+        public:
             const bool isPrimary;
 
             /**
@@ -92,7 +93,7 @@ namespace direct_bt {
 
             GATTService(const std::shared_ptr<DBTDevice> &device, const bool isPrimary,
                         const uint16_t startHandle, const uint16_t endHandle, std::shared_ptr<const uuid_t> type)
-            : device(device), isPrimary(isPrimary), startHandle(startHandle), endHandle(endHandle), type(type), characteristicList() {
+            : wbr_device(device), isPrimary(isPrimary), startHandle(startHandle), endHandle(endHandle), type(type), characteristicList() {
                 characteristicList.reserve(10);
             }
 
@@ -103,6 +104,8 @@ namespace direct_bt {
                 return std::string(JAVA_DBT_PACKAGE "DBTGattService");
             }
 
+            std::shared_ptr<DBTDevice> getDevice() const { return wbr_device.lock(); }
+
             std::string toString() const;
     };