Introduce phantom weak handles in the API and use them internally for debug info

src/debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 576 matching lines @@
 int Debug::ArchiveSpacePerThread() {
   return sizeof(ThreadLocal);
 }
 
 
 ScriptCache::ScriptCache(Isolate* isolate) : HashMap(HashMap::PointersMatch),
                                              isolate_(isolate) {
   Heap* heap = isolate_->heap();
   HandleScope scope(isolate_);
 
-  // Perform two GCs to get rid of all unreferenced scripts. The first GC gets
-  // rid of all the cached script wrappers and the second gets rid of the
-  // scripts which are no longer referenced.
-  heap->CollectAllGarbage(Heap::kMakeHeapIterableMask, "ScriptCache");
+  // Perform a GC to get rid of all unreferenced scripts.
   heap->CollectAllGarbage(Heap::kMakeHeapIterableMask, "ScriptCache");
 
   // Scan heap for Script objects.
   HeapIterator iterator(heap);
   DisallowHeapAllocation no_allocation;
 
   for (HeapObject* obj = iterator.next(); obj != NULL; obj = iterator.next()) {
     if (obj->IsScript() && Script::cast(obj)->HasValidSource()) {
       Add(Handle<Script>(Script::cast(obj)));
     }
@@ skipping 76 matching lines @@
   // Clear the weak handle.
   GlobalHandles::Destroy(location);
 }
 
 
 void Debug::HandleWeakDebugInfo(
     const v8::WeakCallbackData<v8::Value, void>& data) {
   Debug* debug = reinterpret_cast<Isolate*>(data.GetIsolate())->debug();
   DebugInfoListNode* node =
       reinterpret_cast<DebugInfoListNode*>(data.GetParameter());
-  // We need to clear all breakpoints associated with the function to restore
-  // original code and avoid patching the code twice later because
-  // the function will live in the heap until next gc, and can be found by
-  // Debug::FindSharedFunctionInfoInScript.
-  BreakLocationIterator it(node->debug_info(), ALL_BREAK_LOCATIONS);
-  it.ClearAllDebugBreak();
-  debug->RemoveDebugInfo(node->debug_info());
+  debug->RemoveDebugInfo(node->debug_info().location());
 #ifdef DEBUG
   for (DebugInfoListNode* n = debug->debug_info_list_;
        n != NULL;
        n = n->next()) {
     DCHECK(n != node);
   }
 #endif
 }
 
 
 DebugInfoListNode::DebugInfoListNode(DebugInfo* debug_info): next_(NULL) {
   // Globalize the request debug info object and make it weak.
   GlobalHandles* global_handles = debug_info->GetIsolate()->global_handles();
   debug_info_ = Handle<DebugInfo>::cast(global_handles->Create(debug_info));
   GlobalHandles::MakeWeak(reinterpret_cast<Object**>(debug_info_.location()),
-                          this,
-                          Debug::HandleWeakDebugInfo);
+                          this, Debug::HandleWeakDebugInfo,
+                          GlobalHandles::Phantom);
 }
 
 
 DebugInfoListNode::~DebugInfoListNode() {
   GlobalHandles::Destroy(reinterpret_cast<Object**>(debug_info_.location()));
 }
 
 
 bool Debug::CompileDebuggerScript(Isolate* isolate, int index) {
   Factory* factory = isolate->factory();
@@ skipping 434 matching lines @@
 
       // Find the break point and clear it.
       BreakLocationIterator it(debug_info, SOURCE_BREAK_LOCATIONS);
       it.FindBreakLocationFromAddress(debug_info->code()->entry() +
           break_point_info->code_position()->value());
       it.ClearBreakPoint(break_point_object);
 
       // If there are no more break points left remove the debug info for this
       // function.
       if (debug_info->GetBreakPointCount() == 0) {
-        RemoveDebugInfo(debug_info);
+        RemoveDebugInfoAndClearFromShared(debug_info);
       }
 
       return;
     }
     node = node->next();
   }
 }
 
 
 void Debug::ClearAllBreakPoints() {
   DebugInfoListNode* node = debug_info_list_;
   while (node != NULL) {
     // Remove all debug break code.
     BreakLocationIterator it(node->debug_info(), ALL_BREAK_LOCATIONS);
     it.ClearAllDebugBreak();
     node = node->next();
   }
 
   // Remove all debug info.
   while (debug_info_list_ != NULL) {
-    RemoveDebugInfo(debug_info_list_->debug_info());
+    RemoveDebugInfoAndClearFromShared(debug_info_list_->debug_info());
   }
 }
 
 
 void Debug::FloodWithOneShot(Handle<JSFunction> function) {
   PrepareForBreakPoints();
 
   // Make sure the function is compiled and has set up the debug info.
   Handle<SharedFunctionInfo> shared(function->shared());
   if (!EnsureDebugInfo(shared, function)) {
@@ skipping 997 matching lines @@
 
   // Add debug info to the list.
   DebugInfoListNode* node = new DebugInfoListNode(*debug_info);
   node->set_next(debug_info_list_);
   debug_info_list_ = node;
 
   return true;
 }
 
 
-void Debug::RemoveDebugInfo(Handle<DebugInfo> debug_info) {
+// This uses the location of a handle to look up the debug info in the debug
+// info list, but it doesn't use the actual debug info for anything.  Therefore
+// if the debug info has been collected by the GC, we can be sure that this
+// method will not attempt to resurrect it.
+void Debug::RemoveDebugInfo(DebugInfo** debug_info) {
   DCHECK(debug_info_list_ != NULL);
   // Run through the debug info objects to find this one and remove it.
   DebugInfoListNode* prev = NULL;
   DebugInfoListNode* current = debug_info_list_;
   while (current != NULL) {
-    if (*current->debug_info() == *debug_info) {
+    if (current->debug_info().location() == debug_info) {
       // Unlink from list. If prev is NULL we are looking at the first element.
       if (prev == NULL) {
         debug_info_list_ = current->next();
       } else {
         prev->set_next(current->next());
       }
-      current->debug_info()->shared()->set_debug_info(
-              isolate_->heap()->undefined_value());
       delete current;
 
       // If there are no more debug info objects there are not more break
       // points.
       has_break_points_ = debug_info_list_ != NULL;
 
       return;
     }
     // Move to next in list.
     prev = current;
     current = current->next();
   }
   UNREACHABLE();
 }
 
 
+void Debug::RemoveDebugInfoAndClearFromShared(Handle<DebugInfo> debug_info) {
+  HandleScope scope(isolate_);
+  Handle<SharedFunctionInfo> shared(debug_info->shared());
+
+  RemoveDebugInfo(debug_info.location());
+
+  shared->set_debug_info(isolate_->heap()->undefined_value());
+}
+
+
 void Debug::SetAfterBreakTarget(JavaScriptFrame* frame) {
   after_break_target_ = NULL;
 
   if (LiveEdit::SetAfterBreakTarget(this)) return;  // LiveEdit did the job.
 
   HandleScope scope(isolate_);
   PrepareForBreakPoints();
 
   // Get the executing function in which the debug break occurred.
   Handle<JSFunction> function(JSFunction::cast(frame->function()));
@@ skipping 74 matching lines @@
       after_break_target_ = Assembler::target_address_at(addr, *code);
     }
   }
 }
 
 
 bool Debug::IsBreakAtReturn(JavaScriptFrame* frame) {
   HandleScope scope(isolate_);
 
   // If there are no break points this cannot be break at return, as
-  // the debugger statement and stack guard bebug break cannot be at
+  // the debugger statement and stack guard debug break cannot be at
   // return.
   if (!has_break_points_) {
     return false;
   }
 
   PrepareForBreakPoints();
 
   // Get the executing function in which the debug break occurred.
   Handle<JSFunction> function(JSFunction::cast(frame->function()));
   Handle<SharedFunctionInfo> shared(function->shared());
@@ skipping 900 matching lines @@
     return scope.Escape(v8::Utils::ToLocal(Handle<String>::cast(json)));
   } else {
     return v8::Utils::ToLocal(response_json_);
   }
 }
 
 
 v8::Handle<v8::Context> MessageImpl::GetEventContext() const {
   Isolate* isolate = event_data_->GetIsolate();
   v8::Handle<v8::Context> context = GetDebugEventContext(isolate);
-  // Isolate::context() may be NULL when "script collected" event occures.
+  // Isolate::context() may be NULL when "script collected" event occurs.
   DCHECK(!context.IsEmpty());
   return context;
 }
 
 
 v8::Debug::ClientData* MessageImpl::GetClientData() const {
   return client_data_;
 }
 
 
@@ skipping 131 matching lines @@
   logger_->DebugEvent("Put", message.text());
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 } }  // namespace v8::internal