[lldb] Add the ability to remove diagnostic callbacks

Add the ability to remove diagnostic callbacks. This is necessary for
diagnostics who's lifetime is tied to objects that can be destroyed.

Differential revision: https://reviews.llvm.org/D143548

Author: JDevlieghere

lldb/include/lldb/Utility/Diagnostics.h

@@ -42,8 +42,10 @@ class Diagnostics {
   void Report(llvm::StringRef message);
 
   using Callback = std::function<llvm::Error(const FileSpec &)>;
+  using CallbackID = uint64_t;
 
-  void AddCallback(Callback callback);
+  CallbackID AddCallback(Callback callback);
+  void RemoveCallback(CallbackID id);
 
   static Diagnostics &Instance();
 
@@ -61,7 +63,21 @@ class Diagnostics {
 
   RotatingLogHandler m_log_handler;
 
-  llvm::SmallVector<Callback, 4> m_callbacks;
+  struct CallbackEntry {
+    CallbackEntry(CallbackID id, Callback callback)
+        : id(id), callback(std::move(callback)) {}
+    CallbackID id;
+    Callback callback;
+  };
+
+  /// Monotonically increasing callback identifier. Unique per Diagnostic
+  /// instance.
+  CallbackID m_callback_id;
+
+  /// List of callback entries.
+  llvm::SmallVector<CallbackEntry, 4> m_callbacks;
+
+  /// Mutex to protect callback list and callback identifier.
   std::mutex m_callbacks_mutex;
 };
 

lldb/source/Utility/Diagnostics.cpp

@@ -43,9 +43,19 @@ Diagnostics::Diagnostics() : m_log_handler(g_num_log_messages) {}
 
 Diagnostics::~Diagnostics() {}
 
-void Diagnostics::AddCallback(Callback callback) {
+Diagnostics::CallbackID Diagnostics::AddCallback(Callback callback) {
   std::lock_guard<std::mutex> guard(m_callbacks_mutex);
-  m_callbacks.push_back(callback);
+  CallbackID id = m_callback_id++;
+  m_callbacks.emplace_back(id, callback);
+  return id;
+}
+
+void Diagnostics::RemoveCallback(CallbackID id) {
+  std::lock_guard<std::mutex> guard(m_callbacks_mutex);
+  m_callbacks.erase(
+      std::remove_if(m_callbacks.begin(), m_callbacks.end(),
+                     [id](const CallbackEntry &e) { return e.id == id; }),
+      m_callbacks.end());
 }
 
 bool Diagnostics::Dump(raw_ostream &stream) {
@@ -84,8 +94,8 @@ Error Diagnostics::Create(const FileSpec &dir) {
   if (Error err = DumpDiangosticsLog(dir))
     return err;
 
-  for (Callback c : m_callbacks) {
-    if (Error err = c(dir))
+  for (CallbackEntry e : m_callbacks) {
+    if (Error err = e.callback(dir))
       return err;
   }