RuntimeTarget refactor - Store weak refs to agents in RuntimeTarget

Summary:
Changelog: [Internal]

Applies to RuntimeTarget → RuntimeAgent the same pattern we use for InstanceTarget → InstanceAgent (D53266708) and PageTarget → PageTargetSession: the target has `weak_ptr`s to its agents/sessions so it can (1) dispatch events to them and (2) assert that they are destroyed before the target itself is destroyed.

In RuntimeTarget this will primarily serve as an event dispatching mechanism from JS (single target) to CDP (multiple sessions), with the addition of threading abstractions in upcoming diffs.

Reviewed By: hoxyq

Differential Revision: D53266706

fbshipit-source-id: 64d7226a1aebf00e0ad178f28101a568e9bc6c53

Author: motiz88

packages/react-native/ReactCommon/jsinspector-modern/InstanceAgent.h

@@ -57,7 +57,7 @@ class InstanceAgent final {
  private:
   FrontendChannel frontendChannel_;
   InstanceTarget& target_;
-  std::unique_ptr<RuntimeAgent> runtimeAgent_;
+  std::shared_ptr<RuntimeAgent> runtimeAgent_;
   SessionState& sessionState_;
 };
 

packages/react-native/ReactCommon/jsinspector-modern/RuntimeTarget.cpp

@@ -11,14 +11,31 @@ namespace facebook::react::jsinspector_modern {
 RuntimeTarget::RuntimeTarget(RuntimeTargetDelegate& delegate)
     : delegate_(delegate) {}
 
-std::unique_ptr<RuntimeAgent> RuntimeTarget::createAgent(
+std::shared_ptr<RuntimeAgent> RuntimeTarget::createAgent(
     FrontendChannel channel,
     SessionState& sessionState) {
-  return std::make_unique<RuntimeAgent>(
+  auto runtimeAgent = std::make_shared<RuntimeAgent>(
       channel,
       *this,
       sessionState,
       delegate_.createAgentDelegate(channel, sessionState));
+  agents_.push_back(runtimeAgent);
+  return runtimeAgent;
+}
+
+void RuntimeTarget::removeExpiredAgents() {
+  // Remove all expired agents.
+  forEachAgent([](auto&) {});
+}
+
+RuntimeTarget::~RuntimeTarget() {
+  removeExpiredAgents();
+
+  // Agents are owned by the session, not by RuntimeTarget, but
+  // they hold a RuntimeTarget& that we must guarantee is valid.
+  assert(
+      agents_.empty() &&
+      "RuntimeAgent objects must be destroyed before their RuntimeTarget. Did you call InstanceTarget::unregisterRuntime()?");
 }
 
 } // namespace facebook::react::jsinspector_modern

packages/react-native/ReactCommon/jsinspector-modern/RuntimeTarget.h

@@ -11,6 +11,7 @@
 #include "RuntimeAgent.h"
 #include "SessionState.h"
 
+#include <list>
 #include <memory>
 
 #ifndef JSINSPECTOR_EXPORT
@@ -59,6 +60,7 @@ class JSINSPECTOR_EXPORT RuntimeTarget final {
   RuntimeTarget(RuntimeTarget&&) = delete;
   RuntimeTarget& operator=(const RuntimeTarget&) = delete;
   RuntimeTarget& operator=(RuntimeTarget&&) = delete;
+  ~RuntimeTarget();
 
   /**
    * Create a new RuntimeAgent that can be used to debug the underlying JS VM.
@@ -69,12 +71,31 @@ class JSINSPECTOR_EXPORT RuntimeTarget final {
    * frontend.
    * \returns The new agent, or nullptr if the runtime is not debuggable.
    */
-  std::unique_ptr<RuntimeAgent> createAgent(
+  std::shared_ptr<RuntimeAgent> createAgent(
       FrontendChannel channel,
       SessionState& sessionState);
 
  private:
   RuntimeTargetDelegate& delegate_;
+  std::list<std::weak_ptr<RuntimeAgent>> agents_;
+
+  /**
+   * Call the given function for every active agent, and clean up any
+   * references to inactive agents.
+   */
+  template <typename Fn>
+  void forEachAgent(Fn&& fn) {
+    for (auto it = agents_.begin(); it != agents_.end();) {
+      if (auto agent = it->lock()) {
+        fn(*agent);
+        ++it;
+      } else {
+        it = agents_.erase(it);
+      }
+    }
+  }
+
+  void removeExpiredAgents();
 };
 
 } // namespace facebook::react::jsinspector_modern