chromecast: trace.py: Add system tracing support

This adds supports for system tracing via trace.py. It is disabled by
default but can be enable via the --systrace parameter. Requesting
system tracing does no harm on devices where it is not available.

This requires switching the way data is read back over the websocket, as
the "ReportEvents" style cannot return data from secondary tracing agents
such as CastTracingAgent.

BUG=786091

Change-Id: I8b5b39c047ae03073d90d462a4febf1770a8ccd5
Reviewed-on: https://chromium-review.googlesource.com/804559
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521750}

chromecast/tools/trace.py

@@ -70,6 +70,12 @@ def _CreateOptionParser():
            'and used as a ring buffer. If this option is omitted then '
            'recording stops when the trace buffer is full.',
       action='store_true')
+  tracing_opts.add_option(
+      '--systrace',
+      help='Enable system tracing.',
+      action='store_true',
+      dest='systrace',
+      default=False)
   parser.add_option_group(tracing_opts)
 
   output_options = optparse.OptionGroup(parser, 'Output options')
@@ -92,7 +98,7 @@ def main():
 
   with Connect(options) as tracing_backend:
     tracing_backend.StartTracing(options.category_filter,
-                                 options.record_continuously)
+                                 options.record_continuously, options.systrace)
     raw_input('Capturing trace. Press Enter to stop...')
     filepath = GetOutputFilePath(options)
     tracing_backend.StopTracing(filepath)

chromecast/tools/tracinglib.py

@@ -43,6 +43,8 @@ class TracingBackend(object):
     self._buffer_usage_reporting_interval = buffer_usage_reporting_interval
     self._included_categories = []
     self._excluded_categories = []
+    self._pending_read_ids = []
+    self._stream_handle = None
 
   def Connect(self):
     """Connect to cast_shell."""
@@ -63,7 +65,8 @@ class TracingBackend(object):
 
   def StartTracing(self,
                    custom_categories=None,
-                   record_continuously=False):
+                   record_continuously=False,
+                   systrace=True):
     """Begin a tracing session on device.
 
     Args:
@@ -77,8 +80,11 @@ class TracingBackend(object):
     req = {
         'method': 'Tracing.start',
         'params': {
-            'transferMode': 'ReportEvents',
+            'transferMode':
+                'ReturnAsStream' if systrace else 'ReportEvents',
             'traceConfig': {
+                'enableSystrace':
+                    systrace,
                 'recordMode':
                     'recordContinuously'
                     if record_continuously else 'recordUntilFull',
@@ -102,19 +108,19 @@ class TracingBackend(object):
     self._socket.settimeout(self._timeout)
     req = {'method': 'Tracing.end'}
     self._SendRequest(req)
-    while self._socket:
-      res = self._ReceiveResponse()
-      has_error = 'error' in res
-      if has_error:
-        logging.error('Tracing error: ' + str(res.get('error')))
-      if has_error or ('method' in res and self._HandleResponse(res)):
-        self._tracing_client = None
-        result = self._tracing_data
-        self._tracing_data = []
-
-        with open(output_file, 'w') as f:
-          json.dump(result, f)
-        return
+
+    with open(output_file, 'w') as f:
+      while self._socket:
+        res = self._ReceiveResponse()
+        has_error = 'error' in res
+        if has_error:
+          logging.error('Tracing error: ' + str(res.get('error')))
+        if has_error or self._HandleResponse(res, f):
+          self._tracing_client = None
+          if not self._stream_handle:
+            json.dump(self._tracing_data, f)
+          self._tracing_data = []
+          return
 
   def _SendRequest(self, req):
     """Sends request to remote devtools.
@@ -126,6 +132,7 @@ class TracingBackend(object):
     self._next_request_id += 1
     data = json.dumps(req)
     self._socket.send(data)
+    return req['id']
 
   def _ReceiveResponse(self):
     """Get response from remote devtools.
@@ -138,7 +145,21 @@ class TracingBackend(object):
       res = json.loads(data)
       return res
 
-  def _HandleResponse(self, res):
+  def _SendReadRequest(self):
+    """Sends a request to read the trace data stream."""
+    req = {
+      'method': 'IO.read',
+      'params': {
+        'handle': self._stream_handle,
+        'size': 32768,
+      }
+    }
+
+    # Send multiple reads to hide request latency.
+    while len(self._pending_read_ids) < 2:
+      self._pending_read_ids.append(self._SendRequest(req))
+
+  def _HandleResponse(self, res, output_file):
     """Handle response from remote devtools.
 
     Args:
@@ -146,6 +167,7 @@ class TracingBackend(object):
     """
     method = res.get('method')
     value = res.get('params', {}).get('value')
+    response_id = res.get('id', None)
     if 'Tracing.dataCollected' == method:
       if type(value) in [str, unicode]:
         self._tracing_data.append(value)
@@ -156,7 +178,20 @@ class TracingBackend(object):
     elif 'Tracing.bufferUsage' == method and self._tracing_client:
       self._tracing_client.BufferUsage(value)
     elif 'Tracing.tracingComplete' == method:
-      return True
+      self._stream_handle = res.get('params', {}).get('stream')
+      if self._stream_handle:
+        self._SendReadRequest()
+      else:
+        return True
+    elif response_id in self._pending_read_ids:
+      self._pending_read_ids.remove(response_id)
+      data = res.get('result', {}).get('data')
+      eof = res.get('result', {}).get('eof')
+      output_file.write(data.encode('utf-8'))
+      if eof:
+        return True
+      else:
+        self._SendReadRequest()
 
   def _ParseCustomCategories(self, custom_categories):
     """Parse a category filter into trace config format"""
@@ -189,7 +224,8 @@ class TracingBackendAndroid(object):
 
   def StartTracing(self,
                    custom_categories=None,
-                   record_continuously=False):
+                   record_continuously=False,
+                   systrace=True):
     """Begin a tracing session on device.
 
     Args: