Add support for TraceEvent before the native library is loaded.

base/android/java/src/org/chromium/base/TraceEvent.java

 // Copyright 2014 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.
 
 package org.chromium.base;
 
 import android.os.Looper;
 import android.os.MessageQueue;
 import android.os.SystemClock;
 import android.util.Log;
 import android.util.Printer;
+
 /**
  * Java mirror of Chrome trace event API. See base/trace_event/trace_event.h. Unlike the native
  * version, Java does not have stack objects, so a TRACE_EVENT() which does both TRACE_EVENT_BEGIN()
  * and TRACE_EVENT_END() in ctor/dtor is not possible.
- * It is OK to use tracing before the native library has loaded, but such traces will
- * be ignored. (Perhaps we could devise to buffer them up in future?).
+ * Note that this class can also be used before the native library is loaded for early tracing.
  */
 @JNINamespace("base::android")
 public class TraceEvent {
-
     private static volatile boolean sEnabled = false;
 
     private static class BasicLooperMonitor implements Printer {
         @Override
         public void println(final String line) {
             if (line.startsWith(">")) {
                 beginHandling(line);
             } else {
                 assert line.startsWith("<");
                 endHandling(line);
@@ skipping 136 matching lines @@
      */
     public static void registerNativeEnabledObserver() {
         nativeRegisterEnabledObserver();
     }
 
     /**
      * Notification from native that tracing is enabled/disabled.
      */
     @CalledByNative
     public static void setEnabled(boolean enabled) {
+        if (!enabled) EarlyTraceEvent.disable();
+
         sEnabled = enabled;
         ThreadUtils.getUiThreadLooper().setMessageLogging(
                 enabled ? LooperMonitorHolder.sInstance : null);
     }
 
     /**
+     * Can be called early during the application initialization so that TraceEvent can be used
+     * before the native library is loaded.
+     */
+    public static void enableEarlyTracing() {
+        EarlyTraceEvent.enable();
+    }
+
+    private static void disableEarlyTracing() {
+        EarlyTraceEvent.disable();
+    }
+
+    /**
      * Enables or disabled Android systrace path of Chrome tracing. If enabled, all Chrome
      * traces will be also output to Android systrace. Because of the overhead of Android
      * systrace, this is for WebView only.
      */
     public static void setATraceEnabled(boolean enabled) {
         if (sEnabled == enabled) return;
         if (enabled) {
             nativeStartATrace();
         } else {
             nativeStopATrace();
         }
     }
 
     /**
      * @return True if tracing is enabled, false otherwise.
      * It is safe to call trace methods without checking if TraceEvent
      * is enabled.
      */
     public static boolean enabled() {
-        return sEnabled;
+        return sEnabled || EarlyTraceEvent.isEnabled();
     }
 
     /**
      * Triggers the 'instant' native trace event with no arguments.
      * @param name The name of the event.
      */
     public static void instant(String name) {
         if (sEnabled) nativeInstant(name, null);
     }
 
@@ skipping 22 matching lines @@
      */
     public static void finishAsync(String name, long id) {
         if (sEnabled) nativeFinishAsync(name, id);
     }
 
     /**
      * Triggers the 'begin' native trace event with no arguments.
      * @param name The name of the event.
      */
     public static void begin(String name) {
-        if (sEnabled) nativeBegin(name, null);
+        if (enabled()) begin(name, null);
     }
 
     /**
      * Triggers the 'begin' native trace event.
      * @param name The name of the event.
      * @param arg  The arguments of the event.
      */
     public static void begin(String name, String arg) {
-        if (sEnabled) nativeBegin(name, arg);
+        if (sEnabled) {
+            nativeBegin(name, arg);
+            return;
+        }
+
+        EarlyTraceEvent.begin(name, arg);
     }
 
     /**
+     * Convenience wrapper around the versions of end() that take string parameters.
+     * @see #begin()
+     */
+    public static void end() {
+        if (enabled()) end(getCallerName(), null);
+    }
+
+    /**
      * Triggers the 'end' native trace event with no arguments.
      * @param name The name of the event.
      */
     public static void end(String name) {
-        if (sEnabled) nativeEnd(name, null);
+        if (enabled()) end(name, null);
     }
 
     /**
      * Triggers the 'end' native trace event.
      * @param name The name of the event.
      * @param arg  The arguments of the event.
      */
     public static void end(String name, String arg) {
+        if (!enabled()) return;
+
+        if (EarlyTraceEvent.end(name, arg)) return;
+
         if (sEnabled) nativeEnd(name, arg);
     }
 
+    static String getCallerName() {
+        // This was measured to take about 1ms on Trygon device.

[dsinclair, 2015/03/16 14:41:23]

nit: No idea what Trygon is ....

And, what was 1ms, the return or having the commented out lines enabled?

[Benoit L, 2015/03/19 16:50:47]

This code is not actually required, so it's gone.

+        StackTraceElement[] stack = java.lang.Thread.currentThread().getStackTrace();
+
+        // Commented out to avoid excess call overhead, but these lines can be useful to debug
+        // exactly where the TraceEvent's client is on the callstack.
+        //  int index = 0;
+        //  while (!stack[index].getClassName().equals(TraceEvent.class.getName())) ++index;
+        //  while (stack[index].getClassName().equals(TraceEvent.class.getName())) ++index;
+        //  System.logW("TraceEvent caller is at stack index " + index);
+
+        // '4' Was derived using the above commented out code snippet.
+        return stack[4].getClassName() + "." + stack[4].getMethodName();
+    }
+
     private static native void nativeRegisterEnabledObserver();
     private static native void nativeStartATrace();
     private static native void nativeStopATrace();
     private static native void nativeInstant(String name, String arg);
     private static native void nativeBegin(String name, String arg);
     private static native void nativeEnd(String name, String arg);
     private static native void nativeBeginToplevel();
     private static native void nativeEndToplevel();
     private static native void nativeStartAsync(String name, long id);
     private static native void nativeFinishAsync(String name, long id);
 }