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Commit dd025de0 authored by Florian Mayer's avatar Florian Mayer
Browse files

Do not cache enabled tags in Java. 

As we are elimating the Binder notifications for the sysprop update for
atrace, we no longer have a callback that can be used to read the new
value of the enabled tags.

@CritivalNative calls are very fast (25 ns) so the overhead of always
going to native code to read the tags is negligible.

Test: flash & boot
Test: adb shell su root atrace -t 10 ss
Test: adb shell su root atrace -t 10 wm

Bug: 137366208

This is a cherry-pick of 9fd21022

Change-Id: I1a07fefd751ee28ca9a632a3d78a2925e8827b9c
Merged-In: I1a07fefd751ee28ca9a632a3d78a2925e8827b9c
parent 168c6090

core/java/android/os/Trace.java

+5 −49
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ import android.annotation.UnsupportedAppUsage; 


import com.android.internal.os.Zygote;



import dalvik.annotation.optimization.CriticalNative;

import dalvik.annotation.optimization.FastNative;



/**
@@ -107,12 +108,15 @@ public final class Trace { 
    private static final int MAX_SECTION_NAME_LEN = 127;



    // Must be volatile to avoid word tearing.

    // This is only kept in case any apps get this by reflection but do not

    // check the return value for null.

    @UnsupportedAppUsage

    private static volatile long sEnabledTags = TRACE_TAG_NOT_READY;



    private static int sZygoteDebugFlags = 0;



    @UnsupportedAppUsage

    @CriticalNative

    private static native long nativeGetEnabledTags();

    private static native void nativeSetAppTracingAllowed(boolean allowed);

    private static native void nativeSetTracingEnabled(boolean allowed);
@@ -128,46 +132,9 @@ public final class Trace { 
    @FastNative

    private static native void nativeAsyncTraceEnd(long tag, String name, int cookie);



    static {

        // We configure two separate change callbacks, one in Trace.cpp and one here.  The

        // native callback reads the tags from the system property, and this callback

        // reads the value that the native code retrieved.  It's essential that the native

        // callback executes first.

        //

        // The system provides ordering through a priority level.  Callbacks made through

        // SystemProperties.addChangeCallback currently have a negative priority, while

        // our native code is using a priority of zero.

        SystemProperties.addChangeCallback(() -> {

            cacheEnabledTags();

            if ((sZygoteDebugFlags & Zygote.DEBUG_JAVA_DEBUGGABLE) != 0) {

                traceCounter(TRACE_TAG_ALWAYS, "java_debuggable", 1);

            }

        });

    }



    private Trace() {

    }



    /**

     * Caches a copy of the enabled-tag bits.  The "master" copy is held by the native code,

     * and comes from the PROPERTY_TRACE_TAG_ENABLEFLAGS property.

     * <p>

     * If the native code hasn't yet read the property, we will cause it to do one-time

     * initialization.  We don't want to do this during class init, because this class is

     * preloaded, so all apps would be stuck with whatever the zygote saw.  (The zygote

     * doesn't see the system-property update broadcasts.)

     * <p>

     * We want to defer initialization until the first use by an app, post-zygote.

     * <p>

     * We're okay if multiple threads call here simultaneously -- the native state is

     * synchronized, and sEnabledTags is volatile (prevents word tearing).

     */

    private static long cacheEnabledTags() {

        long tags = nativeGetEnabledTags();

        sEnabledTags = tags;

        return tags;

    }



    /**

     * Returns true if a trace tag is enabled.

     *
@@ -178,10 +145,7 @@ public final class Trace { 
     */

    @UnsupportedAppUsage

    public static boolean isTagEnabled(long traceTag) {

        long tags = sEnabledTags;

        if (tags == TRACE_TAG_NOT_READY) {

            tags = cacheEnabledTags();

        }

        long tags = nativeGetEnabledTags();

        return (tags & traceTag) != 0;

    }
@@ -210,10 +174,6 @@ public final class Trace { 
    @UnsupportedAppUsage

    public static void setAppTracingAllowed(boolean allowed) {

        nativeSetAppTracingAllowed(allowed);



        // Setting whether app tracing is allowed may change the tags, so we update the cached

        // tags here.

        cacheEnabledTags();

    }



    /**
@@ -227,10 +187,6 @@ public final class Trace { 
    public static void setTracingEnabled(boolean enabled, int debugFlags) {

        nativeSetTracingEnabled(enabled);

        sZygoteDebugFlags = debugFlags;



        // Setting whether tracing is enabled may change the tags, so we update the cached tags

        // here.

        cacheEnabledTags();

    }



    /**

core/jni/android_os_Trace.cpp

+5 −7
Original line number Diff line number Diff line
@@ -50,10 +50,6 @@ inline static void withString(JNIEnv* env, jstring jstr, F callback) { 
    callback(buffer.data());

}



static jlong android_os_Trace_nativeGetEnabledTags(JNIEnv*, jclass) {

    return atrace_get_enabled_tags();

}



static void android_os_Trace_nativeTraceCounter(JNIEnv* env, jclass,

        jlong tag, jstring nameStr, jlong value) {

    withString(env, nameStr, [tag, value](char* str) {
@@ -96,9 +92,6 @@ static void android_os_Trace_nativeSetTracingEnabled(JNIEnv*, jclass, jboolean e 


static const JNINativeMethod gTraceMethods[] = {

    /* name, signature, funcPtr */

    { "nativeGetEnabledTags",

            "()J",

            (void*)android_os_Trace_nativeGetEnabledTags },

    { "nativeSetAppTracingAllowed",

            "(Z)V",

            (void*)android_os_Trace_nativeSetAppTracingAllowed },
@@ -123,6 +116,11 @@ static const JNINativeMethod gTraceMethods[] = { 
    { "nativeAsyncTraceEnd",

            "(JLjava/lang/String;I)V",

            (void*)android_os_Trace_nativeAsyncTraceEnd },



    // ----------- @CriticalNative  ----------------

    { "nativeGetEnabledTags",

            "()J",

            (void*)atrace_get_enabled_tags },

};



int register_android_os_Trace(JNIEnv* env) {