Add in some infrastructure to make tracing of logical requests broken over async callbacks easier.

remoting/base/tracer.cc

Index: remoting/base/tracer.cc
diff --git a/remoting/base/tracer.cc b/remoting/base/tracer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c9df2f0d30fa6a651f4ad2fcf4e62e320a57d681
--- /dev/null
+++ b/remoting/base/tracer.cc
@@ -0,0 +1,144 @@
+// Copyright (c) 2010 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 "remoting/base/tracer.h"
+
+#include <list>
+
+#include "base/basictypes.h"
+#include "base/condition_variable.h"
+#include "base/message_loop.h"
+#include "base/rand_util.h"
+#include "base/ref_counted.h"
+#include "base/stl_util-inl.h"
+#include "base/thread.h"
+#include "base/time.h"
+
+namespace remoting {
+
+namespace {
+
+class OutputLogger {
+ public:
+  OutputLogger()
+      : thread_("logging_thread"),
+        stopped_(false),
+        wake_(&lock_) {
+    thread_.Start();
+    thread_.message_loop()->PostTask(
+        FROM_HERE,
+        NewRunnableMethod(this, &OutputLogger::PrintLogs));
+  }
+
+  void OutputTrace(TraceBuffer* buffer) {
+    scoped_ptr<TraceBuffer> buffer_ref_(buffer);
+    AutoLock l(lock_);
+
+    // Drop messages if we're overwhelming the logger.
+    if (buffers_.size() < 10) {
+      buffers_.push_front(buffer_ref_.release());
+      wake_.Signal();
+    } else {
+      // TODO(ajwong): Remove this cause it just overwhelms the logging more.
+      LOG(WARNING) << "Message dropped.";
+    }
+  }
+
+  void LogOneTrace(TraceBuffer* buffer) {
+    LOG(INFO) << "Trace: " << buffer->name();
+    base::Time last_timestamp;
+    for (int i = 0; i < buffer->record_size(); ++i) {
+      const TraceRecord& record = buffer->record(i);
+      base::Time timestamp = base::Time::FromInternalValue(record.timestamp());
+      if (i == 0) {
+        LOG(INFO) << "  TS: " << record.timestamp()
+                  << " msg: " << record.annotation();
+      } else {
+        base::TimeDelta delta = timestamp - last_timestamp;
+        LOG(INFO) << "  TS: " << record.timestamp()
+                  << " msg: " << record.annotation()
+                  << " [ " << delta.InMilliseconds() << "ms ]";
+      }
+      last_timestamp = timestamp;
+    }
+  }
+
+  void PrintLogs() {
+    while(!stopped_) {
+      TraceBuffer* buffer = NULL;
+      {
+        AutoLock l(lock_);
+        if (buffers_.size() == 0) {
+          wake_.Wait();
+        }
+        // Check again since we might have woken for a stop signal.
+        if (buffers_.size() != 0) {
+          buffer = buffers_.back();
+          buffers_.pop_back();
+        }
+      }
+
+      if (buffer) {
+        LogOneTrace(buffer);
+        delete buffer;
+      }
+    }
+  }
+
+ private:
+  friend struct DefaultSingletonTraits<OutputLogger>;
+
+  ~OutputLogger() {
+    {
+      AutoLock l(lock_);
+      stopped_ = true;
+      wake_.Signal();
+    }
+
+    thread_.Stop();
+    STLDeleteElements(&buffers_);
+  }
+
+  Lock lock_;
+  base::Thread thread_;
+  bool stopped_;
+  ConditionVariable wake_;
+  std::list<TraceBuffer*> buffers_;
+};
+
+}  // namespace
+
+Tracer::Tracer(const std::string& name, double sample_percent) {
+  if (sample_percent > base::RandDouble()) {
+    buffer_.reset(new TraceBuffer());
+    buffer_->set_name(name);
+  }
+}
+
+void Tracer::PrintString(const std::string& s) {
+  AutoLock l(lock_);
+  if (!buffer_.get()) {
+    return;
+  }
+
+  TraceRecord* record = buffer_->add_record();
+  record->set_annotation(s);
+  record->set_timestamp(base::Time::Now().ToInternalValue());
+
+  // Take the pointer for the current messageloop as identifying for the
+  // current thread.
+  record->set_thread_id(static_cast<uint64>(PlatformThread::CurrentId()));
+}
+
+Tracer::~Tracer() {
+  AutoLock l(lock_);
+
+  if (buffer_.get()) {
+    Singleton<OutputLogger>::get()->OutputTrace(buffer_.release());
+  }
+}
+
+}  // namespace remoting
+
+DISABLE_RUNNABLE_METHOD_REFCOUNT(remoting::OutputLogger);