[Android] [Java] Process 创建+控制+分析 经验浅谈

无论是Android亦或者Java中或多或少需要调用底层的一些命令，执行一些参数；

此时我们需要用到Java的Process来创建一个子进程，之所以是子进程是因为此进程依赖于发起创建请求的进程，如果发起者被Kill那个子进程也将Kill。

对于Process相信使用过的朋友一定不会陌生，它具有如下特点：

1.创建简单

2.控制难

3.容易导致无法创建子进程

4.如果是多线程那么很有可能造成内存溢出

以上现象如果你只是偶尔使用一次，创建一个进程或许你什么都没有感觉到，但是如果你使用了多线程，进行了大量的创建，以上问题你都会遇到。

相关：http://blog.csdn.net/qiujuer/article/details/38142273，http://blog.csdn.net/qiujuer/article/details/38086071

这两个星期一直在研究上面的问题，我要做的软件是在Android中进行TraceRoute，由于手机不可能完全Root所以不能采用JNI来发送ICMP请求的方式，最终只能使用创建进程方式进行；具体实现思路是：使用PING命令来PING百度等地址，在PING命令中加入TTL，得到每一次的IP地址，当IP地址与目标IP地址符合时退出，并且还需要单独PING一次每一跳的延迟和丢包。

单线程：PING 百度 TTL=1 =》 得到IP，PING IP 得到延迟丢包，改变TTL，进行下一次PING，直到所得到的IP与目标（百度）一样时停止。按照上面的思路一次需要创建两个子进程，一般到百度时TTL大约为12跳左右，所以就是2*12=24个子进程；如果是在单线程下简单明了，但是速度慢，整个过程大约需要1分钟左右。

多线程：同时发起3个线程进行3跳测试TTL=（1，2，3），测试完成后测试下一批数据TTL=（4，5，6），如果也是12跳的话，那么也是24个子进程，但是整体耗时将会为1/3.可见此时效率较高。

但是多线程需要考虑的是线程的同步问题，以及得到数据后的写入问题，这些赞不谈，只谈进程问题。经过我的测试假如现在测试100个网站的TraceRoute数据，在上层控制一次测试4个网站，底层实现并发3个线程，此时在一定时间内将会同时存在34个进程。按照平均每个网站12跳来算：122100=240个子进程，需要的子线程为12100=120个。

这个时候问题来了，假如现在程序子进程不正常了，遇到了一个一定的问题导致进程无法执行完成，此时你的现象是：一个子进程卡住，随后创建的所有子进程都卡住。假如最上层线程做了任务时间限制，那么到时间后将会尝试销毁，但是你会发现无法销毁，所持有的线程也不会销毁。但是上层以为销毁掉了，然后继续进行下一批的数据测试，此时你的线程数量会逐渐增加，如果100任务下来你的线程或许会达到34100=1200如果有前期没有这样的情况那个就是一半：600个线程左右，如果后期还有任务将会继续增加但是却永远不会销毁，但是我们知道JVM的内存是有限的，所以此时将会出现内存溢出。

以上就是我遇到的问题，我最先改为了等待线程完全返回后再进行下一批数据测试，此时内存溢出是解决了，但是任务却一直卡住在哪里了，永远也不走。我就在想要解决这一的问题需要解决根本上的问题才行，经过研究我发现在程序创建了子进程后JVM将会创建一个子进程管理线程：“ProcessManager”：

正常情况下该线程状态为Native，但是如果创建大量子进程后有可能会出现此线程为Monitor状态，过一段时间后所有创建子进程的线程状态也将会变为Monitor状态，然后将一直死锁，后面创建线程也是继续死锁，无法继续。

通过查看ProcessManager源码发现，其中启动了一个线程用于监听子进程状态，同时管理子进程，比如输出消息以及关闭子进程等操作，具体如下：

/** * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package java.lang; import java.io.File; import java.io.FileDescriptor; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.lang.ref.ReferenceQueue; import java.lang.ref.WeakReference; import java.util.HashMap; import java.util.Map; import java.util.Arrays; import java.util.logging.Logger; import java.util.logging.Level; /*** * Manages child processes. * * <p>Harmony's native implementation (for comparison purposes): * http://tinyurl.com/3ytwuq */ final class ProcessManager { /*** * constant communicated from native code indicating that a * child died, but it was unable to determine the status */ private static final int WAIT_STATUS_UNKNOWN = -1; /*** * constant communicated from native code indicating that there * are currently no children to wait for */ private static final int WAIT_STATUS_NO_CHILDREN = -2; /*** * constant communicated from native code indicating that a wait() * call returned -1 and set an undocumented (and hence unexpected) errno */ private static final int WAIT_STATUS_STRANGE_ERRNO = -3; /*** * Initializes native static state. */ static native void staticInitialize(); static { staticInitialize(); } /*** * Map from pid to Process. We keep weak references to the Process objects * and clean up the entries when no more external references are left. The * process objects themselves don't require much memory, but file * descriptors (associated with stdin/out/err in this case) can be * a scarce resource. */ private final Map<Integer, ProcessReference> processReferences = new HashMap<Integer, ProcessReference>(); /*** Keeps track of garbage-collected Processes. */ private final ProcessReferenceQueue referenceQueue = new ProcessReferenceQueue(); private ProcessManager() { // Spawn a thread to listen for signals from child processes. Thread processThread = new Thread(ProcessManager.class.getName()) { @Override public void run() { watchChildren(); } }; processThread.setDaemon(true); processThread.start(); } /*** * Kills the process with the given ID. * * @parm pid ID of process to kill */ private static native void kill(int pid) throws IOException; /*** * Cleans up after garbage collected processes. Requires the lock on the * map. */ void cleanUp() { ProcessReference reference; while ((reference = referenceQueue.poll()) != null) { synchronized (processReferences) { processReferences.remove(reference.processId); } } } /*** * Listens for signals from processes and calls back to * {@link #onExit(int,int)}. */ native void watchChildren(); /*** * Called by {@link #watchChildren()} when a child process exits. * * @param pid ID of process that exited * @param exitValue value the process returned upon exit */ void onExit(int pid, int exitValue) { ProcessReference processReference = null; synchronized (processReferences) { cleanUp(); if (pid >= 0) { processReference = processReferences.remove(pid); } else if (exitValue == WAIT_STATUS_NO_CHILDREN) { if (processReferences.isEmpty()) { /** * There are no eligible children; wait for one to be * added. The wait() will return due to the * notifyAll() call below. */ try { processReferences.wait(); } catch (InterruptedException ex) { // This should never happen. throw new AssertionError("unexpected interrupt"); } } else { /** * A new child was spawned just before we entered * the synchronized block. We can just fall through * without doing anything special and land back in * the native wait(). */ } } else { // Something weird is happening; abort! throw new AssertionError("unexpected wait() behavior"); } } if (processReference != null) { ProcessImpl process = processReference.get(); if (process != null) { process.setExitValue(exitValue); } } } /*** * Executes a native process. Fills in in, out, and err and returns the * new process ID upon success. */ static native int exec(String[] command, String[] environment, String workingDirectory, FileDescriptor in, FileDescriptor out, FileDescriptor err, boolean redirectErrorStream) throws IOException; /*** * Executes a process and returns an object representing it. */ Process exec(String[] taintedCommand, String[] taintedEnvironment, File workingDirectory, boolean redirectErrorStream) throws IOException { // Make sure we throw the same exceptions as the RI. if (taintedCommand == null) { throw new NullPointerException(); } if (taintedCommand.length == 0) { throw new IndexOutOfBoundsException(); } // Handle security and safety by copying mutable inputs and checking them. String[] command = taintedCommand.clone(); String[] environment = taintedEnvironment != null ? taintedEnvironment.clone() : null; SecurityManager securityManager = System.getSecurityManager(); if (securityManager != null) { securityManager.checkExec(command[0]); } // Check we're not passing null Strings to the native exec. for (String arg : command) { if (arg == null) { throw new NullPointerException(); } } // The environment is allowed to be null or empty, but no element may be null. if (environment != null) { for (String env : environment) { if (env == null) { throw new NullPointerException(); } } } FileDescriptor in = new FileDescriptor(); FileDescriptor out = new FileDescriptor(); FileDescriptor err = new FileDescriptor(); String workingPath = (workingDirectory == null) ? null : workingDirectory.getPath(); // Ensure onExit() doesn't access the process map before we add our // entry. synchronized (processReferences) { int pid; try { pid = exec(command, environment, workingPath, in, out, err, redirectErrorStream); } catch (IOException e) { IOException wrapper = new IOException("Error running exec()." + " Command: " + Arrays.toString(command) + " Working Directory: " + workingDirectory + " Environment: " + Arrays.toString(environment)); wrapper.initCause(e); throw wrapper; } ProcessImpl process = new ProcessImpl(pid, in, out, err); ProcessReference processReference = new ProcessReference(process, referenceQueue); processReferences.put(pid, processReference); /** * This will wake up the child monitor thread in case there * weren't previously any children to wait on. */ processReferences.notifyAll(); return process; } } static class ProcessImpl extends Process { /*** Process ID. */ final int id; final InputStream errorStream; /*** Reads output from process. */ final InputStream inputStream; /*** Sends output to process. */ final OutputStream outputStream; /*** The process's exit value. */ Integer exitValue = null; final Object exitValueMutex = new Object(); ProcessImpl(int id, FileDescriptor in, FileDescriptor out, FileDescriptor err) { this.id = id; this.errorStream = new ProcessInputStream(err); this.inputStream = new ProcessInputStream(in); this.outputStream = new ProcessOutputStream(out); } public void destroy() { try { kill(this.id); } catch (IOException e) { Logger.getLogger(Runtime.class.getName()).log(Level.FINE, "Failed to destroy process " + id + ".", e); } } public int exitValue() { synchronized (exitValueMutex) { if (exitValue == null) { throw new IllegalThreadStateException( "Process has not yet terminated."); } return exitValue; } } public InputStream getErrorStream() { return this.errorStream; } public InputStream getInputStream() { return this.inputStream; } public OutputStream getOutputStream() { return this.outputStream; } public int waitFor() throws InterruptedException { synchronized (exitValueMutex) { while (exitValue == null) { exitValueMutex.wait(); } return exitValue; } } void setExitValue(int exitValue) { synchronized (exitValueMutex) { this.exitValue = exitValue; exitValueMutex.notifyAll(); } } @Override public String toString() { return "Process[id=" + id + "]"; } } static class ProcessReference extends WeakReference<ProcessImpl> { final int processId; public ProcessReference(ProcessImpl referent, ProcessReferenceQueue referenceQueue) { super(referent, referenceQueue); this.processId = referent.id; } } static class ProcessReferenceQueue extends ReferenceQueue<ProcessImpl> { @Override public ProcessReference poll() { // Why couldn't they get the generics right on ReferenceQueue? :( Object reference = super.poll(); return (ProcessReference) reference; } } static final ProcessManager instance = new ProcessManager(); /*** Gets the process manager. */ static ProcessManager getInstance() { return instance; } /*** Automatically closes fd when collected. */ private static class ProcessInputStream extends FileInputStream { private FileDescriptor fd; private ProcessInputStream(FileDescriptor fd) { super(fd); this.fd = fd; } @Override public void close() throws IOException { try { super.close(); } finally { synchronized (this) { if (fd != null && fd.valid()) { try { ProcessManager.close(fd); } finally { fd = null; } } } } } } /*** Automatically closes fd when collected. */ private static class ProcessOutputStream extends FileOutputStream { private FileDescriptor fd; private ProcessOutputStream(FileDescriptor fd) { super(fd); this.fd = fd; } @Override public void close() throws IOException { try { super.close(); } finally { synchronized (this) { if (fd != null && fd.valid()) { try { ProcessManager.close(fd); } finally { fd = null; } } } } } } /*** Closes the given file descriptor. */ private static native void close(FileDescriptor fd) throws IOException; } 

在其中有一个“ native void watchChildren();”方法，此方法为线程主方法，具体实现可以看看JNI，在其中回调了方法：“ void onExit(int pid, int exitValue);” 在方法中：

void onExit(int pid, int exitValue) { ProcessReference processReference = null; synchronized (processReferences) { cleanUp(); if (pid >= 0) { processReference = processReferences.remove(pid); } else if (exitValue == WAIT_STATUS_NO_CHILDREN) { if (processReferences.isEmpty()) { /** * There are no eligible children; wait for one to be * added. The wait() will return due to the * notifyAll() call below. */ try { processReferences.wait(); } catch (InterruptedException ex) { // This should never happen. throw new AssertionError("unexpected interrupt"); } } else { /** * A new child was spawned just before we entered * the synchronized block. We can just fall through * without doing anything special and land back in * the native wait(). */ } } else { // Something weird is happening; abort! throw new AssertionError("unexpected wait() behavior"); } } if (processReference != null) { ProcessImpl process = processReference.get(); if (process != null) { process.setExitValue(exitValue); } } } 

此方法作用是删除子进程队列中子进程同时通知子进程 ProcessImpl已完成。
但是在方法：“watchChildren（）”中如果出现System.in缓冲期满的情况那么进程将无法正常结束，它将一直等待缓冲区有空间存在，而缓冲区又是公共区间，如果一个出现等待那么后续子进程也将全部等待，如果缓冲区无法清空，那么所有子进程将会全部死锁掉。这就是导致子进程卡死的凶手。

知道问题关键点那么就会有人想办法解决，例如：

//...读取数据... process.waitFor(); //....再次读取 

这样的方式看似很好，但是你有没有想过有些数据无法及时返回，所以在 waitfor()之前读取很有可能没有数据导致进行 waitfor()等待，这时我们可以看看源码：

public int waitFor() throws InterruptedException { synchronized (exitValueMutex) { while (exitValue == null) { exitValueMutex.wait(); } return exitValue; } } void setExitValue(int exitValue) { synchronized (exitValueMutex) { this.exitValue = exitValue; exitValueMutex.notifyAll(); } } 

这里可以看见假如没有退出值将会进行等待，直到通知发生，但是通知想要发生必须要靠“ ProcessManager ”线程来告诉你。但是假如在等待过程中出现了大量的数据，导致 System.IN 满了，此时“ ProcessManager ”线程很傻很傻的进入了等待状态中，也将无法进行通知，而这边也就无法往下走，无法到达第二次读取，所以第二次读取就很随机了，在大量数据下第二次读取基本上就是摆设，也就是说无法正常的执行，最终也将导致死锁。
解决办法也很简单，创建线程后我们可以创建一个线程来专门读取信息，直到“ProcessManager”线程通知结束的时候，才退出线程。

首先我们看看Process提供的“exitValue()”方法：

public int exitValue() { synchronized (exitValueMutex) { if (exitValue == null) { throw new IllegalThreadStateException( "Process has not yet terminated."); } return exitValue; } } 

可见在” exitValue “没有值时将会抛出异常而不会阻塞，所以可以得出：” exitValue() “与” waitfor() “都可以用于判断线程是否完成，但是一个是阻塞的一个是不阻塞的方法，在线程中当然使用不阻塞的来完成我们的工作：

/** * 实例化一个ProcessModel * * @param process Process */ private ProcessModel(Process process) { //init this.process = process; //get out = process.getOutputStream(); in = process.getInputStream(); err = process.getErrorStream(); //in if (in != null) { isInReader = new InputStreamReader(in); bInReader = new BufferedReader(isInReader, BUFFER_LENGTH); } sbReader = new StringBuilder(); //start read thread readThread(); } .................... //读取结果 private void read() { String str; //read In try { while ((str = bInReader.readLine()) != null) { sbReader.append(str); sbReader.append(BREAK_LINE); } } catch (Exception e) { e.printStackTrace(); Logs.e(TAG, e.getMessage()); } } /** * 启动线程进行异步读取结果 */ private void readThread() { Thread thread = new Thread(new Runnable() { @Override public void run() { // while (true) { try { process.exitValue(); //read last read(); break; } catch (IllegalThreadStateException e) { read(); } StaticFunction.sleepIgnoreInterrupt(300); } //read end int len; if (in != null) { try { while ((len = in.read(BUFFER)) > 0) { Logs.d(TAG, String.valueOf(len)); } } catch (IOException e) { e.printStackTrace(); Logs.e(TAG, e.getMessage()); } } //close close(); //done isDone = true; } }); thread.setName("DroidTestAgent.Test.TestModel.ProcessModel:ReadThread"); thread.setDaemon(true); thread.start(); } 

当创建进程后把进程丢进我建立的类中实例化为一个进程管理类，随后启动线程，线程执行中调用进程的” exitValue()“ ，如果异常就进入读取数据，直到不异常时再次读取一次最后数据，随后退出循环，退出后还读取了一次底层的数据（这个其实可以不用要,纯属心理作用！）。最后写入完成标记。其中” StaticFunction.sleepIgnoreInterrupt(300); “是我写的静态方法用于休眠等待而已，也就是 Sleep ，只不过加入了 try catch 。
当然光是读取IN流是不行的，还有Error流，这个时候就需要两个线程来完成，一个也行。不过我为了简单采用了：ProcessBuilder类创建进程并重定向了错误流到IN流中，这样简化了操作。

而使用ProcessBuilder类需要注意的是同一个ProcessBuilder实例创建子进程的时候是需要进行线程同步操作的，因为如果并发操作将会导致进程参数错误等现象发生，所以建议加上线程互斥来实现，但是不建议重复创建ProcessBuilder实例，创建那么多实例，何不把所有子进程放在一个ProcessBuilder实例里边。减少内存消耗啊，手机伤不起啊。

有必要提出的是，当线程判断结束的时候，也就是退出值（exitvalue）有值得时候此时其实在”ProcessManager“线程中已经杀掉了进程了，此时在进程中其实没有此进程了，有的也就是执行后的数据流而已。所以正常结束情况下无需自己调用”destroy()“方法，调用后将会触发异常，说没有找到此进程。

public void destroy() { try { kill(this.id); } catch (IOException e) { Logger.getLogger(Runtime.class.getName()).log(Level.FINE, "Failed to destroy process " + id + ".", e); } } 

终于讲完了，累啊；

最后给大家分享我自己弄得一个类（ProcessModel），大家喜欢就直接拿去，如果有好的建议希望大家提出来：

import com.droidtestagent.journal.Logs; import com.droidtestagent.util.StaticFunction; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.OutputStream; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * Create By Qiujuer * 2014-08-05 * <p/> * 执行命令行语句进程管理封装 */ public class ProcessModel { private static final String TAG = "ProcessModel"; //换行符 private static final String BREAK_LINE; //错误缓冲 private static final byte[] BUFFER; //缓冲区大小 private static final int BUFFER_LENGTH; //创建进程时需要互斥进行 private static final Lock lock = new ReentrantLock(); //ProcessBuilder private static final ProcessBuilder prc; final private Process process; final private InputStream in; final private InputStream err; final private OutputStream out; final private StringBuilder sbReader; private BufferedReader bInReader = null; private InputStreamReader isInReader = null; private boolean isDone; /** * 静态变量初始化 */ static { BREAK_LINE = "\n"; BUFFER_LENGTH = 128; BUFFER = new byte[BUFFER_LENGTH]; prc = new ProcessBuilder(); } /** * 实例化一个ProcessModel * * @param process Process */ private ProcessModel(Process process) { //init this.process = process; //get out = process.getOutputStream(); in = process.getInputStream(); err = process.getErrorStream(); //in if (in != null) { isInReader = new InputStreamReader(in); bInReader = new BufferedReader(isInReader, BUFFER_LENGTH); } sbReader = new StringBuilder(); //start read thread readThread(); } /** * 执行命令 * * @param params 命令参数 eg: "/system/bin/ping", "-c", "4", "-s", "100","www.qiujuer.net" */ public static ProcessModel create(String... params) { Process process = null; try { lock.lock(); process = prc.command(params) .redirectErrorStream(true) .start(); } catch (IOException e) { e.printStackTrace(); } finally { //sleep 100 StaticFunction.sleepIgnoreInterrupt(100); lock.unlock(); } if (process == null) return null; return new ProcessModel(process); } /** * 通过Android底层实现进程关闭 * * @param process 进程 */ public static void kill(Process process) { int pid = getProcessId(process); if (pid != 0) { try { android.os.Process.killProcess(pid); } catch (Exception e) { try { process.destroy(); } catch (Exception ex) { //ex.printStackTrace(); } } } } /** * 获取进程的ID * * @param process 进程 * @return id */ public static int getProcessId(Process process) { String str = process.toString(); try { int i = str.indexOf("=") + 1; int j = str.indexOf("]"); str = str.substring(i, j); return Integer.parseInt(str); } catch (Exception e) { return 0; } } //读取结果 private void read() { String str; //read In try { while ((str = bInReader.readLine()) != null) { sbReader.append(str); sbReader.append(BREAK_LINE); } } catch (Exception e) { e.printStackTrace(); Logs.e(TAG, e.getMessage()); } } /** * 启动线程进行异步读取结果 */ private void readThread() { Thread thread = new Thread(new Runnable() { @Override public void run() { //while to end while (true) { try { process.exitValue(); //read last read(); break; } catch (IllegalThreadStateException e) { read(); } StaticFunction.sleepIgnoreInterrupt(300); } //read end int len; if (in != null) { try { while ((len = in.read(BUFFER)) > 0) { Logs.d(TAG, String.valueOf(len)); } } catch (IOException e) { e.printStackTrace(); Logs.e(TAG, e.getMessage()); } } //close close(); //done isDone = true; } }); thread.setName("DroidTestAgent.Test.TestModel.ProcessModel:ReadThread"); thread.setDaemon(true); thread.start(); } /** * 获取执行结果 * * @return 结果 */ public String getResult() { //waite process setValue try { process.waitFor(); } catch (Exception e) { e.printStackTrace(); Logs.e(TAG, e.getMessage()); } //until startRead en while (true) { if (isDone) break; StaticFunction.sleepIgnoreInterrupt(100); } //return if (sbReader.length() == 0) return null; else return sbReader.toString(); } /** * 关闭所有流 */ private void close() { //close out if (out != null) { try { out.close(); } catch (IOException e) { e.printStackTrace(); } } //err if (err != null) { try { err.close(); } catch (IOException e) { e.printStackTrace(); } } //in if (in != null) { try { in.close(); } catch (IOException e) { e.printStackTrace(); } } if (isInReader != null) { try { isInReader.close(); } catch (IOException e) { e.printStackTrace(); } } if (bInReader != null) { try { bInReader.close(); } catch (IOException e) { e.printStackTrace(); } } } /** * 销毁 */ public void destroy() { //process try { process.destroy(); } catch (Exception ex) { kill(process); } } }