// 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/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?).
*/
@JNINamespace("base::android")
public class TraceEvent {
private static volatile boolean sEnabled = false;
private static class BasicLooperMonitor implements Printer {
private static final String DISPATCH_EVENT_NAME =
"Looper.dispatchMessage";
@Override
public void println(final String line) {
if (line.startsWith(">")) {
beginHandling(line);
} else {
assert line.startsWith("<");
endHandling(line);
}
}
void beginHandling(final String line) {
TraceEvent.begin(DISPATCH_EVENT_NAME, line);
}
void endHandling(final String line) {
TraceEvent.end(DISPATCH_EVENT_NAME);
}
}
/**
* A class that records, traces and logs statistics about the UI thead's Looper.
* The output of this class can be used in a number of interesting ways:
* <p>
* <ol><li>
* When using chrometrace, there will be a near-continuous line of
* measurements showing both event dispatches as well as idles;
* </li><li>
* Logging messages are output for events that run too long on the
* event dispatcher, making it easy to identify problematic areas;
* </li><li>
* Statistics are output whenever there is an idle after a non-trivial
* amount of activity, allowing information to be gathered about task
* density and execution cadence on the Looper;
* </li></ol>
* <p>
* The class attaches itself as an idle handler to the main Looper, and
* monitors the execution of events and idle notifications. Task counters
* accumulate between idle notifications and get reset when a new idle
* notification is received.
*/
private static final class IdleTracingLooperMonitor extends BasicLooperMonitor
implements MessageQueue.IdleHandler {
// Tags for dumping to logcat or TraceEvent
private static final String TAG = "TraceEvent.LooperMonitor";
private static final String IDLE_EVENT_NAME = "Looper.queueIdle";
// Calculation constants
private static final long FRAME_DURATION_MILLIS = 1000L / 60L; // 60 FPS
// A reasonable threshold for defining a Looper event as "long running"
private static final long MIN_INTERESTING_DURATION_MILLIS =
FRAME_DURATION_MILLIS;
// A reasonable threshold for a "burst" of tasks on the Looper
private static final long MIN_INTERESTING_BURST_DURATION_MILLIS =
MIN_INTERESTING_DURATION_MILLIS * 3;
// Stats tracking
private long mLastIdleStartedAt = 0L;
private long mLastWorkStartedAt = 0L;
private int mNumTasksSeen = 0;
private int mNumIdlesSeen = 0;
private int mNumTasksSinceLastIdle = 0;
// State
private boolean mIdleMonitorAttached = false;
// Called from within the begin/end methods only.
// This method can only execute on the looper thread, because that is
// the only thread that is permitted to call Looper.myqueue().
private final void syncIdleMonitoring() {
if (sEnabled && !mIdleMonitorAttached) {
// approximate start time for computational purposes
mLastIdleStartedAt = SystemClock.elapsedRealtime();
Looper.myQueue().addIdleHandler(this);
mIdleMonitorAttached = true;
Log.v(TAG, "attached idle handler");
} else if (mIdleMonitorAttached && !sEnabled) {
Looper.myQueue().removeIdleHandler(this);
mIdleMonitorAttached = false;
Log.v(TAG, "detached idle handler");
}
}
@Override
final void beginHandling(final String line) {
// Close-out any prior 'idle' period before starting new task.
if (mNumTasksSinceLastIdle == 0) {
TraceEvent.end(IDLE_EVENT_NAME);
}
mLastWorkStartedAt = SystemClock.elapsedRealtime();
syncIdleMonitoring();
super.beginHandling(line);
}
@Override
final void endHandling(final String line) {
final long elapsed = SystemClock.elapsedRealtime()
- mLastWorkStartedAt;
if (elapsed > MIN_INTERESTING_DURATION_MILLIS) {
traceAndLog(Log.WARN, "observed a task that took "
+ elapsed + "ms: " + line);
}
super.endHandling(line);
syncIdleMonitoring();
mNumTasksSeen++;
mNumTasksSinceLastIdle++;
}
private static void traceAndLog(int level, String message) {
TraceEvent.instant("TraceEvent.LooperMonitor:IdleStats", message);
Log.println(level, TAG, message);
}
@Override
public final boolean queueIdle() {
final long now = SystemClock.elapsedRealtime();
if (mLastIdleStartedAt == 0) mLastIdleStartedAt = now;
final long elapsed = now - mLastIdleStartedAt;
mNumIdlesSeen++;
TraceEvent.begin(IDLE_EVENT_NAME, mNumTasksSinceLastIdle + " tasks since last idle.");
if (elapsed > MIN_INTERESTING_BURST_DURATION_MILLIS) {
// Dump stats
String statsString = mNumTasksSeen + " tasks and "
+ mNumIdlesSeen + " idles processed so far, "
+ mNumTasksSinceLastIdle + " tasks bursted and "
+ elapsed + "ms elapsed since last idle";
traceAndLog(Log.DEBUG, statsString);
}
mLastIdleStartedAt = now;
mNumTasksSinceLastIdle = 0;
return true; // stay installed
}
}
// Holder for monitor avoids unnecessary construction on non-debug runs
private static final class LooperMonitorHolder {
private static final BasicLooperMonitor sInstance =
CommandLine.getInstance().hasSwitch(BaseSwitches.ENABLE_IDLE_TRACING) ?
new IdleTracingLooperMonitor() : new BasicLooperMonitor();
}
/**
* 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() {
boolean enabled = nativeTraceEnabled();
if (sEnabled == enabled) return;
sEnabled = enabled;
ThreadUtils.getUiThreadLooper().setMessageLogging(
enabled() ? LooperMonitorHolder.sInstance : null);
}
/**
* 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 (enabled) {
nativeStartATrace();
} else {
nativeStopATrace();
}
setEnabledToMatchNative();
}
/**
* @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;
}
/**
* 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);
}
/**
* Triggers the 'instant' native trace event.
* @param name The name of the event.
* @param arg The arguments of the event.
*/
public static void instant(String name, String arg) {
if (sEnabled) nativeInstant(name, arg);
}
/**
* Convenience wrapper around the versions of startAsync() that take string parameters.
* @param id The id of the asynchronous event.
* @see #begin()
*/
public static void startAsync(long id) {
if (sEnabled) nativeStartAsync(getCallerName(), id, null);
}
/**
* Triggers the 'start' native trace event with no arguments.
* @param name The name of the event.
* @param id The id of the asynchronous event.
*/
public static void startAsync(String name, long id) {
if (sEnabled) nativeStartAsync(name, id, null);
}
/**
* Triggers the 'start' native trace event.
* @param name The name of the event.
* @param id The id of the asynchronous event.
* @param arg The arguments of the event.
*/
public static void startAsync(String name, long id, String arg) {
if (sEnabled) nativeStartAsync(name, id, arg);
}
/**
* Convenience wrapper around the versions of finishAsync() that take string parameters.
* @param id The id of the asynchronous event.
* @see #begin()
*/
public static void finishAsync(long id) {
if (sEnabled) nativeFinishAsync(getCallerName(), id, null);
}
/**
* Triggers the 'finish' native trace event with no arguments.
* @param name The name of the event.
* @param id The id of the asynchronous event.
*/
public static void finishAsync(String name, long id) {
if (sEnabled) nativeFinishAsync(name, id, null);
}
/**
* Triggers the 'finish' native trace event.
* @param name The name of the event.
* @param id The id of the asynchronous event.
* @param arg The arguments of the event.
*/
public static void finishAsync(String name, long id, String arg) {
if (sEnabled) nativeFinishAsync(name, id, 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.
*
* Note that the overhead is at ms or sub-ms order. Don't use this when millisecond accuracy
* is desired.
*/
public static void begin() {
if (sEnabled) nativeBegin(getCallerName(), null);
}
/**
* 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);
}
/**
* 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);
}
/**
* Convenience wrapper around the versions of end() that take string parameters.
* @see #begin()
*/
public static void end() {
if (sEnabled) nativeEnd(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);
}
/**
* 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 (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 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 nativeStartAsync(String name, long id, String arg);
private static native void nativeFinishAsync(String name, long id, String arg);
}