Increase plugin life time

A plugin is created when it is first needed and destroyed when the FP device
is destroyed. This allows the plugins to keep state during long running
operations such as presenting a UI query.

PiperOrigin-RevId: 543502491

fastpair/repository/BUILD

@@ -40,8 +40,10 @@ cc_library(
     visibility = ["//fastpair:__subpackages__"],
     deps = [
         "//fastpair/common",
+        "//internal/base",
         "//internal/platform:logging",
         "//internal/platform:types",
+        "@com_google_absl//absl/functional:any_invocable",
     ],
 )
 

fastpair/repository/fast_pair_device_repository.cc

@@ -47,7 +47,10 @@ void FastPairDeviceRepository::RemoveDevice(const FastPairDevice* device) {
   // Tasks running in the background may still be referencing `device`. Defering
   // the destruction to the background thread should prevent use-after-free
   // errors.
-  executor_->Execute([fast_pair_device = std::move(fast_pair_device)]() {
+  executor_->Execute([this, fast_pair_device = std::move(fast_pair_device)]() {
+    for (auto* callback : observers_.GetObservers()) {
+      (*callback)(*fast_pair_device);
+    }
     NEARBY_LOGS(VERBOSE) << "Destroyed FP device: " << fast_pair_device;
   });
 }

fastpair/repository/fast_pair_device_repository.h

@@ -19,7 +19,9 @@
 #include <optional>
 #include <vector>
 
+#include "absl/functional/any_invocable.h"
 #include "fastpair/common/fast_pair_device.h"
+#include "internal/base/observer_list.h"
 #include "internal/platform/mutex.h"
 #include "internal/platform/single_thread_executor.h"
 
@@ -29,6 +31,12 @@ namespace fastpair {
 // Owner of `FastPairDevice` instances.
 class FastPairDeviceRepository {
  public:
+  // Called on the background thread right before `device` is destroyed.
+  // The callbacks are not called when FastPairDeviceRepository is
+  // destructing.
+  using RemoveDeviceCallback =
+      absl::AnyInvocable<void(const FastPairDevice& device)>;
+
   explicit FastPairDeviceRepository(SingleThreadExecutor* executor)
       : executor_(executor) {}
 
@@ -46,12 +54,20 @@ class FastPairDeviceRepository {
   // or BLE.
   std::optional<FastPairDevice*> FindDevice(absl::string_view mac_address);
 
+  void AddObserver(RemoveDeviceCallback* observer) {
+    observers_.AddObserver(observer);
+  }
+  void RemoveObserver(RemoveDeviceCallback* observer) {
+    observers_.RemoveObserver(observer);
+  }
+
  private:
   // Removes `device` from `devices_`.
   std::unique_ptr<FastPairDevice> ExtractDevice(const FastPairDevice* device);
   Mutex mutex_;
   SingleThreadExecutor* executor_;
   std::vector<std::unique_ptr<FastPairDevice>> devices_ ABSL_GUARDED_BY(mutex_);
+  ObserverList<RemoveDeviceCallback> observers_;
 };
 
 }  // namespace fastpair

fastpair/repository/fast_pair_device_repository_test.cc

@@ -100,6 +100,19 @@ TEST(FastPairDeviceRepositoryTest, RemovingNonRegisteredDeviceIsSafe) {
   EXPECT_FALSE(repo.FindDevice(kBleAddress).has_value());
 }
 
+TEST(FastPairDeviceRepositoryTest, RemovingDeviceCallsCallback) {
+  SingleThreadExecutor executor;
+  FastPairDeviceRepository repo(&executor);
+  FastPairDevice* device = repo.AddDevice(std::make_unique<FastPairDevice>(
+      kModelId, kBleAddress, Protocol::kFastPairInitialPairing));
+  FastPairDeviceRepository::RemoveDeviceCallback callback =
+      [&](const FastPairDevice& device) {};
+  repo.AddObserver(&callback);
+  repo.RemoveDevice(device);
+
+  EXPECT_FALSE(repo.FindDevice(kBleAddress).has_value());
+}
+
 }  // namespace
 
 }  // namespace fastpair