Revert of [tracing] Simplify logic of MemoryDumpManager

base/trace_event/memory_dump_manager.cc

Index: base/trace_event/memory_dump_manager.cc
diff --git a/base/trace_event/memory_dump_manager.cc b/base/trace_event/memory_dump_manager.cc
index f5c3c4feb4b91c8e6835a154239cc55979e476ef..cbce21021c08a599fa6f6d23db007de8d8bad7b4 100644
--- a/base/trace_event/memory_dump_manager.cc
+++ b/base/trace_event/memory_dump_manager.cc
@@ -193,16 +193,17 @@
   if (dumper_registrations_ignored_for_testing_)
     return;
 
-  scoped_refptr<MemoryDumpProviderInfo> mdpinfo =
-      new MemoryDumpProviderInfo(mdp, name, task_runner, options);
-
-  {
-    AutoLock lock(lock_);
-    bool already_registered = !dump_providers_.insert(mdpinfo).second;
-    // This actually happen in some tests which don't have a clean tear-down
-    // path for RenderThreadImpl::Init().
-    if (already_registered)
-      return;
+  MemoryDumpProviderInfo mdp_info(mdp, name, task_runner, options);
+  AutoLock lock(lock_);
+  auto iter_new = dump_providers_.insert(mdp_info);
+
+  // If there was a previous entry, replace it with the new one. This is to deal
+  // with the case where a dump provider unregisters itself and then re-
+  // registers before a memory dump happens, so its entry was still in the
+  // collection but flagged |unregistered|.
+  if (!iter_new.second) {
+    dump_providers_.erase(iter_new.first);
+    dump_providers_.insert(mdp_info);
   }
 
   if (heap_profiling_enabled_)
@@ -221,7 +222,7 @@
 
   auto mdp_iter = dump_providers_.begin();
   for (; mdp_iter != dump_providers_.end(); ++mdp_iter) {
-    if ((*mdp_iter)->dump_provider == mdp)
+    if (mdp_iter->dump_provider == mdp)
       break;
   }
 
@@ -235,18 +236,12 @@
   // Otherwise, it is not possible to guarantee that its unregistration is
   // race-free. If you hit this DCHECK, your MDP has a bug.
   DCHECK(!subtle::NoBarrier_Load(&memory_tracing_enabled_) ||
-         ((*mdp_iter)->task_runner &&
-          (*mdp_iter)->task_runner->BelongsToCurrentThread()))
-      << "MemoryDumpProvider \"" << (*mdp_iter)->name << "\" attempted to "
+         (mdp_iter->task_runner &&
+          mdp_iter->task_runner->BelongsToCurrentThread()))
+      << "MemoryDumpProvider \"" << mdp_iter->name << "\" attempted to "
       << "unregister itself in a racy way. Please file a crbug.";
 
-  // The MDPInfo instance can still be referenced by the
-  // |ProcessMemoryDumpAsyncState.pending_dump_providers|. For this reason
-  // the MDPInfo is flagged as disabled. It will cause ContinueAsyncProcessDump
-  // to just skip it, without actually invoking the |mdp|, which might be
-  // destroyed by the caller soon after this method returns.
-  (*mdp_iter)->disabled = true;
-  dump_providers_.erase(mdp_iter);
+  mdp_iter->unregistered = true;
 }
 
 void MemoryDumpManager::RequestGlobalDump(
@@ -301,9 +296,9 @@
   scoped_ptr<ProcessMemoryDumpAsyncState> pmd_async_state;
   {
     AutoLock lock(lock_);
-    pmd_async_state.reset(
-        new ProcessMemoryDumpAsyncState(args, dump_providers_, session_state_,
-                                        callback, dump_thread_->task_runner()));
+    pmd_async_state.reset(new ProcessMemoryDumpAsyncState(
+        args, dump_providers_.begin(), session_state_, callback,
+        dump_thread_->task_runner()));
   }
 
   TRACE_EVENT_WITH_FLOW0(kTraceCategory, "MemoryDumpManager::CreateProcessDump",
@@ -313,7 +308,7 @@
   // Start the thread hop. |dump_providers_| are kept sorted by thread, so
   // ContinueAsyncProcessDump will hop at most once per thread (w.r.t. thread
   // affinity specified by the MemoryDumpProvider(s) in RegisterDumpProvider()).
-  ContinueAsyncProcessDump(pmd_async_state.release());
+  ContinueAsyncProcessDump(std::move(pmd_async_state));
 }
 
 // At most one ContinueAsyncProcessDump() can be active at any time for a given
@@ -323,103 +318,128 @@
 // means of subsequent PostTask(s).
 //
 // 1) Prologue:
-//   - If this was the last hop, create a trace event, add it to the trace
-//     and finalize (invoke callback).
+//   - Check if the dump provider is disabled, if so skip the dump.
 //   - Check if we are on the right thread. If not hop and continue there.
-//   - Check if the dump provider is disabled, if so skip the dump.
 // 2) Invoke the dump provider's OnMemoryDump() (unless skipped).
 // 3) Epilogue:
-//   - Unregister the dump provider if it failed too many times consecutively.
-//   - Pop() the MDP from the |pending_dump_providers| list, eventually
-//     destroying the MDPInfo if that was unregistered in the meantime.
+//  - Unregister the dump provider if it failed too many times consecutively.
+//  - Advance the |next_dump_provider| iterator to the next dump provider.
+//  - If this was the last hop, create a trace event, add it to the trace
+//    and finalize (invoke callback).
+
 void MemoryDumpManager::ContinueAsyncProcessDump(
-    ProcessMemoryDumpAsyncState* owned_pmd_async_state) {
+    scoped_ptr<ProcessMemoryDumpAsyncState> pmd_async_state) {
   // Initalizes the ThreadLocalEventBuffer to guarantee that the TRACE_EVENTs
   // in the PostTask below don't end up registering their own dump providers
   // (for discounting trace memory overhead) while holding the |lock_|.
   TraceLog::GetInstance()->InitializeThreadLocalEventBufferIfSupported();
 
-  // In theory |owned_pmd_async_state| should be a scoped_ptr. The only reason
-  // why it isn't is because of the corner case logic of |did_post_task| below,
-  // which needs to take back the ownership of the |pmd_async_state| when a
-  // thread goes away and consequently the PostTask() fails.
-  // Unfortunately, PostTask() destroys the scoped_ptr arguments upon failure
-  // to prevent accidental leaks. Using a scoped_ptr would prevent us to to
-  // skip the hop and move on. Hence the manual naked -> scoped ptr juggling.
-  auto pmd_async_state = make_scoped_ptr(owned_pmd_async_state);
-  owned_pmd_async_state = nullptr;
-
-  if (pmd_async_state->pending_dump_providers.empty())
-    return FinalizeDumpAndAddToTrace(std::move(pmd_async_state));
-
-  // Read MemoryDumpProviderInfo thread safety considerations in
-  // memory_dump_manager.h when accessing |mdpinfo| fields.
-  MemoryDumpProviderInfo* mdpinfo =
-      pmd_async_state->pending_dump_providers.back().get();
-
-  // If the dump provider did not specify a thread affinity, dump on
-  // |dump_thread_|. Note that |dump_thread_| might have been Stop()-ed at this
-  // point (if tracing was disabled in the meanwhile). In such case the
-  // PostTask() below will fail, but |task_runner| should always be non-null.
-  SingleThreadTaskRunner* task_runner = mdpinfo->task_runner.get();
-  if (!task_runner)
-    task_runner = pmd_async_state->dump_thread_task_runner.get();
-
-  if (!task_runner->BelongsToCurrentThread()) {
-    // It's time to hop onto another thread.
-    const bool did_post_task = task_runner->PostTask(
-        FROM_HERE, Bind(&MemoryDumpManager::ContinueAsyncProcessDump,
-                        Unretained(this), Unretained(pmd_async_state.get())));
-    if (did_post_task) {
-      // Ownership is tranferred to the next ContinueAsyncProcessDump().
-      ignore_result(pmd_async_state.release());
-      return;
+  const uint64_t dump_guid = pmd_async_state->req_args.dump_guid;
+  const char* dump_provider_name = nullptr;
+
+  // Pid of the target process being dumped. Often kNullProcessId (= current
+  // process), non-zero when the coordinator process creates dumps on behalf
+  // of child processes (see crbug.com/461788).
+  ProcessId pid;
+
+  // DO NOT put any LOG() statement in the locked sections, as in some contexts
+  // (GPU process) LOG() ends up performing PostTask/IPCs.
+  MemoryDumpProvider* mdp;
+  bool skip_dump = false;
+  {
+    AutoLock lock(lock_);
+
+    auto mdp_info = pmd_async_state->next_dump_provider;
+    mdp = mdp_info->dump_provider;
+    dump_provider_name = mdp_info->name;
+    pid = mdp_info->options.target_pid;
+
+    // If the dump provider did not specify a thread affinity, dump on
+    // |dump_thread_|.
+    SingleThreadTaskRunner* task_runner = mdp_info->task_runner.get();
+    if (!task_runner)
+      task_runner = pmd_async_state->dump_thread_task_runner.get();
+
+    // |dump_thread_| might have been Stop()-ed at this point (if tracing was
+    // disabled in the meanwhile). In such case the PostTask() below will fail.
+    // |task_runner|, however, should always be non-null.
+    DCHECK(task_runner);
+
+    if (mdp_info->disabled || mdp_info->unregistered) {
+      skip_dump = true;
+    } else if (!task_runner->BelongsToCurrentThread()) {
+      // It's time to hop onto another thread.
+
+      // Copy the callback + arguments just for the unlikley case in which
+      // PostTask fails. In such case the Bind helper will destroy the
+      // pmd_async_state and we must keep a copy of the fields to notify the
+      // abort.
+      MemoryDumpCallback callback = pmd_async_state->callback;
+      scoped_refptr<SingleThreadTaskRunner> callback_task_runner =
+          pmd_async_state->callback_task_runner;
+
+      const bool did_post_task = task_runner->PostTask(
+          FROM_HERE, Bind(&MemoryDumpManager::ContinueAsyncProcessDump,
+                          Unretained(this), Passed(&pmd_async_state)));
+      if (did_post_task)
+        return;
+
+      // The thread is gone. At this point the best thing we can do is to
+      // disable the dump provider and abort this dump.
+      mdp_info->disabled = true;
+      return AbortDumpLocked(callback, callback_task_runner, dump_guid);
     }
-    // The thread is gone. Skip the dump provider and keep going.
-    mdpinfo->disabled = true;
-  }
-
-  // At this point wither we are on the right thread (|mdpinfo.task_runner|)
-  // to access mdp fields, or the right thread is gone (and |disabled| == true).
-
-  if (!mdpinfo->disabled) {
-    // Invoke the dump provider.
+  }  // AutoLock(lock_)
+
+  // Invoke the dump provider without holding the |lock_|.
+  bool finalize = false;
+  bool dump_successful = false;
+
+  if (!skip_dump) {
     TRACE_EVENT_WITH_FLOW1(kTraceCategory,
                            "MemoryDumpManager::ContinueAsyncProcessDump",
-                           TRACE_ID_MANGLE(pmd_async_state->req_args.dump_guid),
+                           TRACE_ID_MANGLE(dump_guid),
                            TRACE_EVENT_FLAG_FLOW_IN | TRACE_EVENT_FLAG_FLOW_OUT,
-                           "dump_provider.name", mdpinfo->name);
-
-    // Pid of the target process being dumped. Often kNullProcessId (= current
-    // process), non-zero when the coordinator process creates dumps on behalf
-    // of child processes (see crbug.com/461788).
-    ProcessId target_pid = mdpinfo->options.target_pid;
-    ProcessMemoryDump* pmd =
-        pmd_async_state->GetOrCreateMemoryDumpContainerForProcess(target_pid);
+                           "dump_provider.name", dump_provider_name);
     MemoryDumpArgs args = {pmd_async_state->req_args.level_of_detail};
-    bool dump_successful = mdpinfo->dump_provider->OnMemoryDump(args, pmd);
-
+    ProcessMemoryDump* process_memory_dump =
+        pmd_async_state->GetOrCreateMemoryDumpContainerForProcess(pid);
+    dump_successful = mdp->OnMemoryDump(args, process_memory_dump);
+  }
+
+  {
+    AutoLock lock(lock_);
+    auto mdp_info = pmd_async_state->next_dump_provider;
     if (dump_successful) {
-      mdpinfo->consecutive_failures = 0;
-    } else {
-      ++mdpinfo->consecutive_failures;
-      if (mdpinfo->consecutive_failures >= kMaxConsecutiveFailuresCount) {
-        mdpinfo->disabled = true;
-        LOG(ERROR) << "MemoryDumpProvider \"" << mdpinfo->name << "\" failed, "
-                   << "possibly due to sandboxing (crbug.com/461788)."
-                   << "Disabling dumper for current process. Try --no-sandbox.";
+      mdp_info->consecutive_failures = 0;
+    } else if (!skip_dump) {
+      ++mdp_info->consecutive_failures;
+      if (mdp_info->consecutive_failures >= kMaxConsecutiveFailuresCount) {
+        mdp_info->disabled = true;
       }
     }
-  }  // if (!mdpinfo->disabled)
-
-  pmd_async_state->pending_dump_providers.pop_back();
-  ContinueAsyncProcessDump(pmd_async_state.release());
+    ++pmd_async_state->next_dump_provider;
+    finalize = pmd_async_state->next_dump_provider == dump_providers_.end();
+
+    if (mdp_info->unregistered)
+      dump_providers_.erase(mdp_info);
+  }
+
+  if (!skip_dump && !dump_successful) {
+    LOG(ERROR) << "MemoryDumpProvider \"" << dump_provider_name << "\" failed, "
+               << "possibly due to sandboxing (crbug.com/461788)."
+               << "Disabling dumper for current process. Try --no-sandbox.";
+  }
+
+  if (finalize)
+    return FinalizeDumpAndAddToTrace(std::move(pmd_async_state));
+
+  ContinueAsyncProcessDump(std::move(pmd_async_state));
 }
 
 // static
 void MemoryDumpManager::FinalizeDumpAndAddToTrace(
     scoped_ptr<ProcessMemoryDumpAsyncState> pmd_async_state) {
-  DCHECK(pmd_async_state->pending_dump_providers.empty());
   const uint64_t dump_guid = pmd_async_state->req_args.dump_guid;
   if (!pmd_async_state->callback_task_runner->BelongsToCurrentThread()) {
     scoped_refptr<SingleThreadTaskRunner> callback_task_runner =
@@ -461,6 +481,20 @@
 
   TRACE_EVENT_NESTABLE_ASYNC_END0(kTraceCategory, "ProcessMemoryDump",
                                   TRACE_ID_MANGLE(dump_guid));
+}
+
+// static
+void MemoryDumpManager::AbortDumpLocked(
+    MemoryDumpCallback callback,
+    scoped_refptr<SingleThreadTaskRunner> task_runner,
+    uint64_t dump_guid) {
+  if (callback.is_null())
+    return;  // There is nothing to NACK.
+
+  // Post the callback even if we are already on the right thread to avoid
+  // invoking the callback while holding the lock_.
+  task_runner->PostTask(FROM_HERE,
+                        Bind(callback, dump_guid, false /* success */));
 }
 
 void MemoryDumpManager::OnTraceLogEnabled() {
@@ -507,6 +541,11 @@
   session_state_ = new MemoryDumpSessionState(stack_frame_deduplicator,
                                               type_name_deduplicator);
 
+  for (auto it = dump_providers_.begin(); it != dump_providers_.end(); ++it) {
+    it->disabled = false;
+    it->consecutive_failures = 0;
+  }
+
   subtle::NoBarrier_Store(&memory_tracing_enabled_, 1);
 
   // TODO(primiano): This is a temporary hack to disable periodic memory dumps
@@ -578,36 +617,31 @@
       task_runner(task_runner),
       options(options),
       consecutive_failures(0),
-      disabled(false) {}
+      disabled(false),
+      unregistered(false) {}
 
 MemoryDumpManager::MemoryDumpProviderInfo::~MemoryDumpProviderInfo() {}
 
-bool MemoryDumpManager::MemoryDumpProviderInfo::Comparator::operator()(
-    const scoped_refptr<MemoryDumpManager::MemoryDumpProviderInfo>& a,
-    const scoped_refptr<MemoryDumpManager::MemoryDumpProviderInfo>& b) const {
-  if (!a || !b)
-    return a.get() < b.get();
+bool MemoryDumpManager::MemoryDumpProviderInfo::operator<(
+    const MemoryDumpProviderInfo& other) const {
+  if (task_runner == other.task_runner)
+    return dump_provider < other.dump_provider;
   // Ensure that unbound providers (task_runner == nullptr) always run last.
-  // Rationale: some unbound dump providers are known to be slow, keep them last
-  // to avoid skewing timings of the other dump providers.
-  return std::tie(a->task_runner, a->dump_provider) >
-         std::tie(b->task_runner, b->dump_provider);
+  return !(task_runner < other.task_runner);
 }
 
 MemoryDumpManager::ProcessMemoryDumpAsyncState::ProcessMemoryDumpAsyncState(
     MemoryDumpRequestArgs req_args,
-    const MemoryDumpProviderInfo::OrderedSet& dump_providers,
+    MemoryDumpProviderInfoSet::iterator next_dump_provider,
     const scoped_refptr<MemoryDumpSessionState>& session_state,
     MemoryDumpCallback callback,
     const scoped_refptr<SingleThreadTaskRunner>& dump_thread_task_runner)
     : req_args(req_args),
+      next_dump_provider(next_dump_provider),
       session_state(session_state),
       callback(callback),
       callback_task_runner(MessageLoop::current()->task_runner()),
-      dump_thread_task_runner(dump_thread_task_runner) {
-  pending_dump_providers.reserve(dump_providers.size());
-  pending_dump_providers.assign(dump_providers.rbegin(), dump_providers.rend());
-}
+      dump_thread_task_runner(dump_thread_task_runner) {}
 
 MemoryDumpManager::ProcessMemoryDumpAsyncState::~ProcessMemoryDumpAsyncState() {
 }