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
17package android.os;
18
19/**
20 * Writes trace events to the system trace buffer.  These trace events can be
21 * collected and visualized using the Systrace tool.
22 *
23 * <p>This tracing mechanism is independent of the method tracing mechanism
24 * offered by {@link Debug#startMethodTracing}.  In particular, it enables
25 * tracing of events that occur across multiple processes.
26 * <p>For information about using the Systrace tool, read <a
27 * href="{@docRoot}tools/debugging/systrace.html">Analyzing Display and Performance
28 * with Systrace</a>.
29 */
30public final class Trace {
31    /*
32     * Writes trace events to the kernel trace buffer.  These trace events can be
33     * collected using the "atrace" program for offline analysis.
34     */
35
36    private static final String TAG = "Trace";
37
38    // These tags must be kept in sync with system/core/include/cutils/trace.h.
39    // They should also be added to frameworks/native/cmds/atrace/atrace.cpp.
40    /** @hide */
41    public static final long TRACE_TAG_NEVER = 0;
42    /** @hide */
43    public static final long TRACE_TAG_ALWAYS = 1L << 0;
44    /** @hide */
45    public static final long TRACE_TAG_GRAPHICS = 1L << 1;
46    /** @hide */
47    public static final long TRACE_TAG_INPUT = 1L << 2;
48    /** @hide */
49    public static final long TRACE_TAG_VIEW = 1L << 3;
50    /** @hide */
51    public static final long TRACE_TAG_WEBVIEW = 1L << 4;
52    /** @hide */
53    public static final long TRACE_TAG_WINDOW_MANAGER = 1L << 5;
54    /** @hide */
55    public static final long TRACE_TAG_ACTIVITY_MANAGER = 1L << 6;
56    /** @hide */
57    public static final long TRACE_TAG_SYNC_MANAGER = 1L << 7;
58    /** @hide */
59    public static final long TRACE_TAG_AUDIO = 1L << 8;
60    /** @hide */
61    public static final long TRACE_TAG_VIDEO = 1L << 9;
62    /** @hide */
63    public static final long TRACE_TAG_CAMERA = 1L << 10;
64    /** @hide */
65    public static final long TRACE_TAG_HAL = 1L << 11;
66    /** @hide */
67    public static final long TRACE_TAG_APP = 1L << 12;
68    /** @hide */
69    public static final long TRACE_TAG_RESOURCES = 1L << 13;
70    /** @hide */
71    public static final long TRACE_TAG_DALVIK = 1L << 14;
72    /** @hide */
73    public static final long TRACE_TAG_RS = 1L << 15;
74    /** @hide */
75    public static final long TRACE_TAG_BIONIC = 1L << 16;
76    /** @hide */
77    public static final long TRACE_TAG_POWER = 1L << 17;
78
79    private static final long TRACE_TAG_NOT_READY = 1L << 63;
80    private static final int MAX_SECTION_NAME_LEN = 127;
81
82    // Must be volatile to avoid word tearing.
83    private static volatile long sEnabledTags = TRACE_TAG_NOT_READY;
84
85    private static native long nativeGetEnabledTags();
86    private static native void nativeTraceCounter(long tag, String name, int value);
87    private static native void nativeTraceBegin(long tag, String name);
88    private static native void nativeTraceEnd(long tag);
89    private static native void nativeAsyncTraceBegin(long tag, String name, int cookie);
90    private static native void nativeAsyncTraceEnd(long tag, String name, int cookie);
91    private static native void nativeSetAppTracingAllowed(boolean allowed);
92    private static native void nativeSetTracingEnabled(boolean allowed);
93
94    static {
95        // We configure two separate change callbacks, one in Trace.cpp and one here.  The
96        // native callback reads the tags from the system property, and this callback
97        // reads the value that the native code retrieved.  It's essential that the native
98        // callback executes first.
99        //
100        // The system provides ordering through a priority level.  Callbacks made through
101        // SystemProperties.addChangeCallback currently have a negative priority, while
102        // our native code is using a priority of zero.
103        SystemProperties.addChangeCallback(new Runnable() {
104            @Override public void run() {
105                cacheEnabledTags();
106            }
107        });
108    }
109
110    private Trace() {
111    }
112
113    /**
114     * Caches a copy of the enabled-tag bits.  The "master" copy is held by the native code,
115     * and comes from the PROPERTY_TRACE_TAG_ENABLEFLAGS property.
116     * <p>
117     * If the native code hasn't yet read the property, we will cause it to do one-time
118     * initialization.  We don't want to do this during class init, because this class is
119     * preloaded, so all apps would be stuck with whatever the zygote saw.  (The zygote
120     * doesn't see the system-property update broadcasts.)
121     * <p>
122     * We want to defer initialization until the first use by an app, post-zygote.
123     * <p>
124     * We're okay if multiple threads call here simultaneously -- the native state is
125     * synchronized, and sEnabledTags is volatile (prevents word tearing).
126     */
127    private static long cacheEnabledTags() {
128        long tags = nativeGetEnabledTags();
129        sEnabledTags = tags;
130        return tags;
131    }
132
133    /**
134     * Returns true if a trace tag is enabled.
135     *
136     * @param traceTag The trace tag to check.
137     * @return True if the trace tag is valid.
138     *
139     * @hide
140     */
141    public static boolean isTagEnabled(long traceTag) {
142        long tags = sEnabledTags;
143        if (tags == TRACE_TAG_NOT_READY) {
144            tags = cacheEnabledTags();
145        }
146        return (tags & traceTag) != 0;
147    }
148
149    /**
150     * Writes trace message to indicate the value of a given counter.
151     *
152     * @param traceTag The trace tag.
153     * @param counterName The counter name to appear in the trace.
154     * @param counterValue The counter value.
155     *
156     * @hide
157     */
158    public static void traceCounter(long traceTag, String counterName, int counterValue) {
159        if (isTagEnabled(traceTag)) {
160            nativeTraceCounter(traceTag, counterName, counterValue);
161        }
162    }
163
164    /**
165     * Set whether application tracing is allowed for this process.  This is intended to be set
166     * once at application start-up time based on whether the application is debuggable.
167     *
168     * @hide
169     */
170    public static void setAppTracingAllowed(boolean allowed) {
171        nativeSetAppTracingAllowed(allowed);
172
173        // Setting whether app tracing is allowed may change the tags, so we update the cached
174        // tags here.
175        cacheEnabledTags();
176    }
177
178    /**
179     * Set whether tracing is enabled in this process.  Tracing is disabled shortly after Zygote
180     * initializes and re-enabled after processes fork from Zygote.  This is done because Zygote
181     * has no way to be notified about changes to the tracing tags, and if Zygote ever reads and
182     * caches the tracing tags, forked processes will inherit those stale tags.
183     *
184     * @hide
185     */
186    public static void setTracingEnabled(boolean enabled) {
187        nativeSetTracingEnabled(enabled);
188
189        // Setting whether tracing is enabled may change the tags, so we update the cached tags
190        // here.
191        cacheEnabledTags();
192    }
193
194    /**
195     * Writes a trace message to indicate that a given section of code has
196     * begun. Must be followed by a call to {@link #traceEnd} using the same
197     * tag.
198     *
199     * @param traceTag The trace tag.
200     * @param methodName The method name to appear in the trace.
201     *
202     * @hide
203     */
204    public static void traceBegin(long traceTag, String methodName) {
205        if (isTagEnabled(traceTag)) {
206            nativeTraceBegin(traceTag, methodName);
207        }
208    }
209
210    /**
211     * Writes a trace message to indicate that the current method has ended.
212     * Must be called exactly once for each call to {@link #traceBegin} using the same tag.
213     *
214     * @param traceTag The trace tag.
215     *
216     * @hide
217     */
218    public static void traceEnd(long traceTag) {
219        if (isTagEnabled(traceTag)) {
220            nativeTraceEnd(traceTag);
221        }
222    }
223
224    /**
225     * Writes a trace message to indicate that a given section of code has
226     * begun. Must be followed by a call to {@link #asyncTraceEnd} using the same
227     * tag. Unlike {@link #traceBegin(long, String)} and {@link #traceEnd(long)},
228     * asynchronous events do not need to be nested. The name and cookie used to
229     * begin an event must be used to end it.
230     *
231     * @param traceTag The trace tag.
232     * @param methodName The method name to appear in the trace.
233     * @param cookie Unique identifier for distinguishing simultaneous events
234     *
235     * @hide
236     */
237    public static void asyncTraceBegin(long traceTag, String methodName, int cookie) {
238        if (isTagEnabled(traceTag)) {
239            nativeAsyncTraceBegin(traceTag, methodName, cookie);
240        }
241    }
242
243    /**
244     * Writes a trace message to indicate that the current method has ended.
245     * Must be called exactly once for each call to {@link #asyncTraceBegin(long, String, int)}
246     * using the same tag, name and cookie.
247     *
248     * @param traceTag The trace tag.
249     * @param methodName The method name to appear in the trace.
250     * @param cookie Unique identifier for distinguishing simultaneous events
251     *
252     * @hide
253     */
254    public static void asyncTraceEnd(long traceTag, String methodName, int cookie) {
255        if (isTagEnabled(traceTag)) {
256            nativeAsyncTraceEnd(traceTag, methodName, cookie);
257        }
258    }
259
260    /**
261     * Writes a trace message to indicate that a given section of code has begun. This call must
262     * be followed by a corresponding call to {@link #endSection()} on the same thread.
263     *
264     * <p class="note"> At this time the vertical bar character '|', newline character '\n', and
265     * null character '\0' are used internally by the tracing mechanism.  If sectionName contains
266     * these characters they will be replaced with a space character in the trace.
267     *
268     * @param sectionName The name of the code section to appear in the trace.  This may be at
269     * most 127 Unicode code units long.
270     */
271    public static void beginSection(String sectionName) {
272        if (isTagEnabled(TRACE_TAG_APP)) {
273            if (sectionName.length() > MAX_SECTION_NAME_LEN) {
274                throw new IllegalArgumentException("sectionName is too long");
275            }
276            nativeTraceBegin(TRACE_TAG_APP, sectionName);
277        }
278    }
279
280    /**
281     * Writes a trace message to indicate that a given section of code has ended. This call must
282     * be preceeded by a corresponding call to {@link #beginSection(String)}. Calling this method
283     * will mark the end of the most recently begun section of code, so care must be taken to
284     * ensure that beginSection / endSection pairs are properly nested and called from the same
285     * thread.
286     */
287    public static void endSection() {
288        if (isTagEnabled(TRACE_TAG_APP)) {
289            nativeTraceEnd(TRACE_TAG_APP);
290        }
291    }
292}
293