Generate globally (cross-process) unique IDs for memory tracing dumps

base/trace_event/trace_event_impl.cc

 // Copyright (c) 2012 The Chromium 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 "base/trace_event/trace_event_impl.h"
 
 #include <algorithm>
 
 #include "base/base_switches.h"
 #include "base/bind.h"
@@ skipping 1890 matching lines @@
   // GpuProcessLogMessageHandler -> PostPendingTask -> TRACE_EVENT ...
   if (thread_is_in_trace_event_.Get())
     return handle;
 
   AutoThreadLocalBoolean thread_is_in_trace_event(&thread_is_in_trace_event_);
 
   DCHECK(name);
   DCHECK(!timestamp.is_null());
 
   if (flags & TRACE_EVENT_FLAG_MANGLE_ID)
-    id ^= process_id_hash_;
+    id = HashEventId(id);
 
   TimeTicks offset_event_timestamp = OffsetTimestamp(timestamp);
   TimeTicks now = flags & TRACE_EVENT_FLAG_EXPLICIT_TIMESTAMP ?
       OffsetNow() : offset_event_timestamp;
   TimeTicks thread_now = ThreadNow();
 
   ThreadLocalEventBuffer* thread_local_event_buffer = NULL;
   // A ThreadLocalEventBuffer needs the message loop
   // - to know when the thread exits;
   // - to handle the final flush.
@@ skipping 248 matching lines @@
   watch_event_callback_ = callback;
 }
 
 void TraceLog::CancelWatchEvent() {
   AutoLock lock(lock_);
   subtle::NoBarrier_Store(&watch_category_, 0);
   watch_event_name_ = "";
   watch_event_callback_.Reset();
 }
 
+uint64 TraceLog::HashEventId(uint64 id) {
+  return id ^ process_id_hash_;
+}
+
+
 void TraceLog::AddMetadataEventsWhileLocked() {
   lock_.AssertAcquired();
 
 #if !defined(OS_NACL)  // NaCl shouldn't expose the process id.
   InitializeMetadataEvent(AddEventToThreadSharedChunkWhileLocked(NULL, false),
                           0,
                           "num_cpus", "number",
                           base::SysInfo::NumberOfProcessors());
 #endif
 
@@ skipping 412 matching lines @@
 }
 
 ScopedTraceBinaryEfficient::~ScopedTraceBinaryEfficient() {
   if (*category_group_enabled_) {
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_group_enabled_,
                                                 name_, event_handle_);
   }
 }
 
 }  // namespace trace_event_internal