Android content shell bringup.

content/public/android/java/org/chromium/content/browser/TraceEvent.java

+// 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.
+
+package org.chromium.content.browser;
+
+import android.os.Looper;
+import android.util.Printer;
+
+// Java mirror of Chrome trace event API.  See
+// base/debug/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?).
+public class TraceEvent {
+
+    private static boolean sEnabled = false;
+
+    private static class LooperTracePrinter implements Printer {
+        private static final String NAME = "Looper.dispatchMessage";
+        @Override
+        public void println(String line) {
+            if (line.startsWith(">>>>>")) {
+                TraceEvent.begin(NAME, line);
+            } else {
+                assert line.startsWith("<<<<<");
+                TraceEvent.end(NAME);
+            }
+        }
+    }
+
+    /**
+     * Calling this will cause enabled() to be updated to match that set on the native side.
+     * The native library must be loaded before calling this method.
+     */
+    public static void setEnabledToMatchNative() {
+        setEnabled(nativeTraceEnabled());
+    }
+
+    /**
+     * Enables or disables tracing.
+     * The native library must be loaded before the first call with enabled == true.
+     */
+    public static synchronized void setEnabled(boolean enabled) {
+        if (enabled) {
+            LibraryLoader.checkIsReady();
+        }
+        if (sEnabled == enabled) {
+            return;
+        }
+        sEnabled = enabled;
+        Looper.getMainLooper().setMessageLogging(enabled ? new LooperTracePrinter() : null);
+    }
+
+    /**
+     * @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;
+    }
+
+    public static void instant(String name) {
+        if (sEnabled) {
+            nativeInstant(name, null);
+        }
+    }
+
+    public static void instant(String name, String arg) {
+        if (sEnabled) {
+            nativeInstant(name, arg);
+        }
+    }
+
+    /**
+     * Convenience wrapper around the versions of begin() that take string parameters.
+     * The name of the event will be derived from the class and function name that call this.
+     * IMPORTANT: if using this version, ensure end() (no parameters) is always called from the
+     * same calling context.
+     */
+    public static void begin() {
+        if (sEnabled) {
+            nativeBegin(getCallerName(), null);
+        }
+    }
+
+    public static void begin(String name) {
+        if (sEnabled) {
+            nativeBegin(name, null);
+        }
+    }
+
+    public static void begin(String name, String arg) {
+        if (sEnabled) {
+            nativeBegin(name, arg);
+        }
+    }
+
+    /**
+     * Convenience wrapper around the versions of end() that take string parameters. See begin()
+     * for more information.
+     */
+    public static void end() {
+        if (sEnabled) {
+            nativeEnd(getCallerName(), null);
+        }
+    }
+
+    public static void end(String name) {
+        if (sEnabled) {
+            nativeEnd(name, null);
+        }
+    }
+
+    public static void end(String name, String arg) {
+        if (sEnabled) {
+            nativeEnd(name, arg);
+        }
+    }
+
+    private static String getCallerName() {
+        // This was measured to take about 1ms on Trygon device.
+        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 boolean nativeTraceEnabled();
+    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);
+}