1 /* 2 * Copyright (C) 2012 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package android.os; 18 19 import android.util.Log; 20 21 /** 22 * Writes trace events to the kernel trace buffer. These trace events can be 23 * collected using the "atrace" program for offline analysis. 24 * 25 * This tracing mechanism is independent of the method tracing mechanism 26 * offered by {@link Debug#startMethodTracing}. In particular, it enables 27 * tracing of events that occur across processes. 28 * 29 * @hide 30 */ 31 public final class Trace { 32 private static final String TAG = "Trace"; 33 34 // These tags must be kept in sync with frameworks/native/include/utils/Trace.h. 35 public static final long TRACE_TAG_NEVER = 0; 36 public static final long TRACE_TAG_ALWAYS = 1L << 0; 37 public static final long TRACE_TAG_GRAPHICS = 1L << 1; 38 public static final long TRACE_TAG_INPUT = 1L << 2; 39 public static final long TRACE_TAG_VIEW = 1L << 3; 40 public static final long TRACE_TAG_WEBVIEW = 1L << 4; 41 public static final long TRACE_TAG_WINDOW_MANAGER = 1L << 5; 42 public static final long TRACE_TAG_ACTIVITY_MANAGER = 1L << 6; 43 public static final long TRACE_TAG_SYNC_MANAGER = 1L << 7; 44 public static final long TRACE_TAG_AUDIO = 1L << 8; 45 public static final long TRACE_TAG_VIDEO = 1L << 9; 46 public static final long TRACE_TAG_CAMERA = 1L << 10; 47 48 public static final int TRACE_FLAGS_START_BIT = 1; 49 public static final String[] TRACE_TAGS = { 50 "Graphics", "Input", "View", "WebView", "Window Manager", 51 "Activity Manager", "Sync Manager", "Audio", "Video", "Camera", 52 }; 53 54 public static final String PROPERTY_TRACE_TAG_ENABLEFLAGS = "debug.atrace.tags.enableflags"; 55 56 // This works as a "not ready" flag because TRACE_TAG_ALWAYS is always set. 57 private static final long TRACE_FLAGS_NOT_READY = 0; 58 59 // Must be volatile to avoid word tearing. 60 private static volatile long sEnabledTags = TRACE_FLAGS_NOT_READY; 61 62 private static native long nativeGetEnabledTags(); 63 private static native void nativeTraceCounter(long tag, String name, int value); 64 private static native void nativeTraceBegin(long tag, String name); 65 private static native void nativeTraceEnd(long tag); 66 67 static { 68 // We configure two separate change callbacks, one in Trace.cpp and one here. The 69 // native callback reads the tags from the system property, and this callback 70 // reads the value that the native code retrieved. It's essential that the native 71 // callback executes first. 72 // 73 // The system provides ordering through a priority level. Callbacks made through 74 // SystemProperties.addChangeCallback currently have a negative priority, while 75 // our native code is using a priority of zero. 76 SystemProperties.addChangeCallback(new Runnable() { 77 @Override public void run() { 78 cacheEnabledTags(); 79 } 80 }); 81 } 82 83 private Trace() { 84 } 85 86 /** 87 * Caches a copy of the enabled-tag bits. The "master" copy is held by the native code, 88 * and comes from the PROPERTY_TRACE_TAG_ENABLEFLAGS property. 89 * <p> 90 * If the native code hasn't yet read the property, we will cause it to do one-time 91 * initialization. We don't want to do this during class init, because this class is 92 * preloaded, so all apps would be stuck with whatever the zygote saw. (The zygote 93 * doesn't see the system-property update broadcasts.) 94 * <p> 95 * We want to defer initialization until the first use by an app, post-zygote. 96 * <p> 97 * We're okay if multiple threads call here simultaneously -- the native state is 98 * synchronized, and sEnabledTags is volatile (prevents word tearing). 99 */ 100 private static long cacheEnabledTags() { 101 long tags = nativeGetEnabledTags(); 102 if (tags == TRACE_FLAGS_NOT_READY) { 103 Log.w(TAG, "Unexpected value from nativeGetEnabledTags: " + tags); 104 // keep going 105 } 106 sEnabledTags = tags; 107 return tags; 108 } 109 110 /** 111 * Returns true if a trace tag is enabled. 112 * 113 * @param traceTag The trace tag to check. 114 * @return True if the trace tag is valid. 115 */ 116 public static boolean isTagEnabled(long traceTag) { 117 long tags = sEnabledTags; 118 if (tags == TRACE_FLAGS_NOT_READY) { 119 tags = cacheEnabledTags(); 120 } 121 return (tags & traceTag) != 0; 122 } 123 124 /** 125 * Writes trace message to indicate the value of a given counter. 126 * 127 * @param traceTag The trace tag. 128 * @param counterName The counter name to appear in the trace. 129 * @param counterValue The counter value. 130 */ 131 public static void traceCounter(long traceTag, String counterName, int counterValue) { 132 if (isTagEnabled(traceTag)) { 133 nativeTraceCounter(traceTag, counterName, counterValue); 134 } 135 } 136 137 /** 138 * Writes a trace message to indicate that a given method has begun. 139 * Must be followed by a call to {@link #traceEnd} using the same tag. 140 * 141 * @param traceTag The trace tag. 142 * @param methodName The method name to appear in the trace. 143 */ 144 public static void traceBegin(long traceTag, String methodName) { 145 if (isTagEnabled(traceTag)) { 146 nativeTraceBegin(traceTag, methodName); 147 } 148 } 149 150 /** 151 * Writes a trace message to indicate that the current method has ended. 152 * Must be called exactly once for each call to {@link #traceBegin} using the same tag. 153 * 154 * @param traceTag The trace tag. 155 */ 156 public static void traceEnd(long traceTag) { 157 if (isTagEnabled(traceTag)) { 158 nativeTraceEnd(traceTag); 159 } 160 } 161 } 162
