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      1 /*
      2  * Copyright (C) 2006 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 dalvik.system;
     18 
     19 import java.io.File;
     20 
     21 /**
     22  * Provides hooks for the zygote to call back into the runtime to perform
     23  * parent or child specific initialization..
     24  *
     25  * @hide
     26  */
     27 public final class ZygoteHooks {
     28     private long token;
     29 
     30     /**
     31      * Called by the zygote prior to every fork. Each call to {@code preFork}
     32      * is followed by a matching call to {@link #postForkChild(int, String)} on the child
     33      * process and {@link #postForkCommon()} on both the parent and the child
     34      * process. {@code postForkCommon} is called after {@code postForkChild} in
     35      * the child process.
     36      */
     37     public void preFork() {
     38         Daemons.stop();
     39         waitUntilAllThreadsStopped();
     40         token = nativePreFork();
     41     }
     42 
     43     /**
     44      * Called by the zygote in the child process after every fork. The debug
     45      * flags from {@code debugFlags} are applied to the child process. The string
     46      * {@code instructionSet} determines whether to use a native bridge.
     47      */
     48     public void postForkChild(int debugFlags, String instructionSet) {
     49         nativePostForkChild(token, debugFlags, instructionSet);
     50 
     51         Math.setRandomSeedInternal(System.currentTimeMillis());
     52     }
     53 
     54     /**
     55      * Called by the zygote in both the parent and child processes after
     56      * every fork. In the child process, this method is called after
     57      * {@code postForkChild}.
     58      */
     59     public void postForkCommon() {
     60         Daemons.start();
     61     }
     62 
     63     private static native long nativePreFork();
     64     private static native void nativePostForkChild(long token, int debugFlags,
     65                                                    String instructionSet);
     66 
     67     /**
     68      * We must not fork until we're single-threaded again. Wait until /proc shows we're
     69      * down to just one thread.
     70      */
     71     private static void waitUntilAllThreadsStopped() {
     72         File tasks = new File("/proc/self/task");
     73         // All Java daemons are stopped already. We're just waiting for their OS counterparts to
     74         // finish as well. This shouldn't take much time so spinning is ok here.
     75         while (tasks.list().length > 1) {
     76           Thread.yield();
     77         }
     78     }
     79 }
     80