i.mx6 Android5.1.1 Zygote
0. 总结：
0.1 相关源码目录：
framework/base/cmds/app_process/app_main.cpp
frameworks/base/core/jni/AndroidRuntime.cpp
frameworks/base/core/jni/com_android_internal_os_ZygoteInit.cpp
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java
0.2 流程总结：
1. init.rc启动进入app_main.cpp
2. app_main.cpp查看init.rc给的相关参数，进行处理进入AndroidRuntime.cpp
3. AndroidRuntime.cpp启动虚拟机，初始化JNI，然后根据函数名通过反射机制加载zygote，进入JAVA层zygote的Zygote.java
4. 注册socket，加载各种资源（类，共享资源，共享库），启动SystemServer服务，循环接收socket，创建新进程
1. native层init.rc(进入zygote)
#名字为zygote的服务，可执行文件路径为/system/bin/app_process，后面几个为带的参数
#建立socket通讯
#运行后，只执行一次的几个服务
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server class main socket zygote stream 660 root system onrestart write /sys/android_power/request_state wake onrestart write /sys/power/state on onrestart restart media onrestart restart netd
2. native层的app_main.cpp
/framework/base/cmds/app_process/app_main.cpp
int main(int argc, char* const argv[]){ //参数argv为：-Xzygote /system/bin --zygote --start-system-server
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0) { // Older kernels don't understand PR_SET_NO_NEW_PRIVS and return // EINVAL. Don't die on such kernels. if (errno != EINVAL) { LOG_ALWAYS_FATAL("PR_SET_NO_NEW_PRIVS failed: %s", strerror(errno)); return 12; } } AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv)); // Process command line arguments // ignore argv[0] argc--; argv++; int i; for (i = 0; i < argc; i++) { if (argv[i][0] != '-') { break; } if (argv[i][1] == '-' && argv[i][2] == 0) { ++i; // Skip --. break; } runtime.addOption(strdup(argv[i])); } // Parse runtime arguments. Stop at first unrecognized option. bool zygote = false; bool startSystemServer = false; bool application = false; String8 niceName; String8 className; ++i; // Skip unused "parent dir" argument. while (i < argc) { const char* arg = argv[i++]; if (strcmp(arg, "--zygote") == 0) {
//这里我们有 zygote = true; niceName = ZYGOTE_NICE_NAME; } else if (strcmp(arg, "--start-system-server") == 0) { startSystemServer = true; //这里我们有 } else if (strcmp(arg, "--application") == 0) { application = true; //这里是进入应用，我们没有 } else if (strncmp(arg, "--nice-name=", 12) == 0) { niceName.setTo(arg + 12); //没有 } else if (strncmp(arg, "--", 2) != 0break; } else { --i; break; } } Vector<String8>if (!className.isEmpty()) { // We're not in zygote mode, the only argument we need to pass // to RuntimeInit is the application argument. // // The Remainder of args get passed to startup class main(). Make // copies of them before we overwrite them with the process name. args.add(application ? String8("application") : String8("tool")); runtime.setClassNameAndArgs(className, argc - i, argv + i); } else { // We're in zygote mode. maybeCreateDalvikCache(); //添加所有参数 } } if (!niceName.isEmpty()) { //没有，不进入 runtime.setArgv0(niceName.string()); set_process_name(niceName.string()); } if (zygote) {
//进入这里，启动zygote
//args为：start-system-server --abi-list=armeabi-v71,armeabi -Xzygote /system/bin --zygote --start-system-server
runtime.start("com.android.internal.os.ZygoteInit", args);
} else if (className) { runtime.start("com.android.internal.os.RuntimeInit", args); } else { fprintf(stderr, "Error: no class name or --zygote supplied.\n"); app_usage(); LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied."); return 10; } }
3. native层的AndroidRuntime
frameworks/base/core/jni/AndroidRuntime.cpp
接着往下看：runtime.start
记住，我们传进来的className为：com.android.internal.os.ZygoteInit
参数为options为：start-system-server --abi-list=armeabi-v71,armeabi -Xzygote /system/bin --zygote --start-system-server
void AndroidRuntime::start(const char* className, const Vector<String8>& options) { ALOGD(">>>>>> START %s uid %d <<<<<<\n", className != NULL ? className : "(unknown)", getuid()); static const String8 startSystemServer("start-system-server"); /* * 'startSystemServer == true' means runtime is obsolete and not run from * init.rc anymore, so we print out the boot start event here. */ for (size_t i = 0; i < options.size(); ++i) { if (options[i] == startSystemServer) {//我们参数有，进入 /* track our progress through the boot sequence */ const int LOG_BOOT_PROGRESS_START = 3000; LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START, ns2ms(systemTime(SYSTEM_TIME_MONOTONIC))); } } //修改环境变量ANDROID_ROOT: /system const char* rootDir = getenv("ANDROID_ROOT"); if (rootDir == NULL) { rootDir = "/system"; if (!hasDir("/system")) { LOG_FATAL("No root directory specified, and /android does not exist."); return; } setenv("ANDROID_ROOT", rootDir, 1); } //const char* kernelHack = getenv("LD_ASSUME_KERNEL"); //ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack); /* start the virtual machine */ //启动虚拟机，以后再分析
JniInvocation jni_invocation; jni_invocation.Init(NULL); JNIEnv* env; if (startVm(&mJavaVM, &env) != 0) { return; } onVmCreated(env); /* * Register android functions.初始化JNI函数 */ if (startReg(env) < 0) { ALOGE("Unable to register all android natives\n"); return; } /* * We want to call main() with a String array with arguments in it. * At present we have two arguments, the class name and an option string. * Create an array to hold them. 下面都是JNI的用法了，具体去查看JNI那章的博客 */ jclass stringClass; jobjectArray strArray; jstring classNameStr; /*
*下面这一串代码就是通过JNI找到ZygoteInit.cpp,然后跳进去，流程是：
*1.找到String类，然后创建一个String = com.android.internal.os.ZygoteInit（这个变量是className参数传进来的）
*2.将com.android.internal.os.ZygoteInit转换成com/android/internal/os/ZygoteInit
*3.查找上面的com/android/internal/os/ZygoteInit这个类中的main函数，
*4.跳入main中
*/
stringClass = env->FindClass("java/lang/String");
assert(stringClass != NULL);
strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL); assert(strArray != NULL); classNameStr = env->NewStringUTF(className); assert(classNameStr != NULL); env->SetObjectArrayElement(strArray, 0, classNameStr); for (size_t i = 0; i < options.size(); ++i) { jstring optionsStr = env->NewStringUTF(options.itemAt(i).string()); assert(optionsStr != NULL); env->SetObjectArrayElement(strArray, i + 1, optionsStr); } /* * Start VM. This thread becomes the main thread of the VM, and will * not return until the VM exits. */ char* slashClassName = toSlashClassName(className); jclass startClass = env->FindClass(slashClassName); if (startClass == NULL) { ALOGE("JavaVM unable to locate class '%s'\n", slashClassName); /* keep going */ } else { jmethodID startMeth = env->GetStaticMethodID(startClass, "main", "([Ljava/lang/String;)V"); if (startMeth == NULL) { ALOGE("JavaVM unable to find main() in '%s'\n", className); /* keep going */ } else {
//在这里通过反射，正式进入JAVA层的zygote：根据上面的注释，可知这里的startClass为Zygote, startMeth为main
//strArry为参数：start-system-server --abi-list=armeabi-v71,armeabi -Xzygote /system/bin --zygote --start-system-server（不是很确定，应该是这个） env->CallStaticVoidMethod(startClass, startMeth, strArray); #if 0 if (env->ExceptionCheck()) threadExitUncaughtException(env); #endif } } free(slashClassName); ALOGD("Shutting down VM\n"); if (mJavaVM->DetachCurrentThread() != JNI_OK) ALOGW("Warning: unable to detach main thread\n"); if (mJavaVM->DestroyJavaVM() != 0) ALOGW("Warning: VM did not shut down cleanly\n"); }
4. JAVA层的Zygote.java
frameworks/base/core/java/com/android/internal/os
ZygoteInit.java函数中的main中
参数如上所分析的argv为：start-system-server --abi-list=armeabi-v71,armeabi -Xzygote /system/bin --zygote --start-system-server
public static void main(String argv[]) { try { // Start profiling the zygote initialization.
// 不懂，以后看 SamplingProfilerIntegration.start(); boolean startSystemServer = false; String socketName = "zygote"; String abiList = null; for (int i = 1; i < argv.length; i++) { if ("start-system-server".equals(argv[i])) { startSystemServer = true; //看上面的参数，这里有 } else if (argv[i].startsWith(ABI_LIST_ARG)) { abiList = argv[i].substring(ABI_LIST_ARG.length()); //--abi-list: 这里有 } else if (argv[i].startsWith(SOCKET_NAME_ARG)) { socketName = argv[i].substring(SOCKET_NAME_ARG.length()); //这个没有 } else { throw new RuntimeException("Unknown command line argument: " + argv[i]); } } if (abiList == null) { throw new RuntimeException("No ABI list supplied."); } //注册zygote的socket，我们socketname为默认的zygote registerZygoteSocket(socketName); EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START, SystemClock.uptimeMillis());
//注意：这个很重要，加载各种资源 preload(); EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END, SystemClock.uptimeMillis()); // Finish profiling the zygote initialization. SamplingProfilerIntegration.writeZygoteSnapshot(); // Do an initial gc to clean up after startup gc(); // Disable tracing so that forked processes do not inherit stale tracing tags from // Zygote. Trace.setTracingEnabled(false); //在这里启动systemserver if (startSystemServer) { startSystemServer(abiList, socketName); } Log.i(TAG, "Accepting command socket connections"); runSelectLoop(abiList); closeServerSocket(); } catch (MethodAndArgsCaller caller) { caller.run(); } catch (RuntimeException ex) { Log.e(TAG, "Zygote died with exception", ex); closeServerSocket(); throw ex; } }
5. JAVA层的preload
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
static void preload() { Log.d(TAG, "begin preload"); preloadClasses(); //加载类 preloadResources(); //加载资源 preloadOpenGL(); //加载OpenGL,这个是跟显示有关的图形库 preloadSharedLibraries(); //加载共享库 // Ask the WebViewFactory to do any initialization that must run in the zygote process, // for memory sharing purposes. WebViewFactory.prepareWebViewInZygote(); //加载？？？，等会再说 Log.d(TAG, "end preload"); //打印log，显示加载完成 }
5.1 加载类preloadClasses
这里用到的反射，忘记了可以看看：语言方面的知识
private static final String PRELOADED_CLASSES = "/system/etc/preloaded-classes";
private static void preloadClasses() { final VMRuntime runtime = VMRuntime.getRuntime(); InputStream is; try { is = new FileInputStream(PRELOADED_CLASSES); //在这里面是预加载的类 } catch (FileNotFoundException e) { Log.e(TAG, "Couldn't find " + PRELOADED_CLASSES + "."); return; } Log.i(TAG, "Preloading classes..."); long startTime = SystemClock.uptimeMillis(); // Drop root perms while running static initializers. setEffectiveGroup(UNPRIVILEGED_GID); setEffectiveUser(UNPRIVILEGED_UID); // Alter the target heap utilization. With explicit GCs this // is not likely to have any effect. float defaultUtilization = runtime.getTargetHeapUtilization(); runtime.setTargetHeapUtilization(0.8f); // Start with a clean slate. System.gc(); runtime.runFinalizationSync(); Debug.startAllocCounting(); try { BufferedReader br = new BufferedReader(new InputStreamReader(is), 256); int count = 0; String line; while ((line = br.readLine()) != null) { //一行一行的读取出来 // Skip comments and blank lines. line = line.trim(); if (line.startsWith("#") || line.equals("")) { continue; } try { if (false) { Log.v(TAG, "Preloading " + line + "..."); } Class.forName(line); //注意：在这里加载的，是通过类名进行反射 if (Debug.getGlobalAllocSize() > PRELOAD_GC_THRESHOLD) { if (false) { Log.v(TAG, " GC at " + Debug.getGlobalAllocSize()); } System.gc(); runtime.runFinalizationSync(); Debug.resetGlobalAllocSize(); } count++; } catch (ClassNotFoundException e) { Log.w(TAG, "Class not found for preloading: " + line); } catch (UnsatisfiedLinkError e) { Log.w(TAG, "Problem preloading " + line + ": " + e); } catch (Throwable t) { Log.e(TAG, "Error preloading " + line + ".", t); if (t instanceof Error) { throw (Error) t; } if (t instanceof RuntimeException) { throw (RuntimeException) t; } throw new RuntimeException(t); } } Log.i(TAG, "...preloaded " + count + " classes in " + (SystemClock.uptimeMillis()-startTime) + "ms."); } catch (IOException e) { Log.e(TAG, "Error reading " + PRELOADED_CLASSES + ".", e); } finally { IoUtils.closeQuietly(is); // Restore default. runtime.setTargetHeapUtilization(defaultUtilization); // Fill in dex caches with classes, fields, and methods brought in by preloading. runtime.preloadDexCaches(); Debug.stopAllocCounting(); // Bring back root. We'll need it later. setEffectiveUser(ROOT_UID); setEffectiveGroup(ROOT_GID); } }
5.2 加载共享资源preloadResources
private static void preloadResources() { final VMRuntime runtime = VMRuntime.getRuntime(); Debug.startAllocCounting(); try { System.gc(); runtime.runFinalizationSync(); mResources = Resources.getSystem(); mResources.startPreloading(); if (PRELOAD_RESOURCES) { Log.i(TAG, "Preloading resources..."); long startTime = SystemClock.uptimeMillis(); TypedArray ar = mResources.obtainTypedArray( com.android.internal.R.array.preloaded_drawables); int N = preloadDrawables(runtime, ar); ar.recycle(); Log.i(TAG, "...preloaded " + N + " resources in " + (SystemClock.uptimeMillis()-startTime) + "ms."); startTime = SystemClock.uptimeMillis(); ar = mResources.obtainTypedArray( com.android.internal.R.array.preloaded_color_state_lists); N = preloadColorStateLists(runtime, ar); ar.recycle(); Log.i(TAG, "...preloaded " + N + " resources in " + (SystemClock.uptimeMillis()-startTime) + "ms."); } mResources.finishPreloading(); } catch (RuntimeException e) { Log.w(TAG, "Failure preloading resources", e); } finally { Debug.stopAllocCounting(); } }
5.3 加载共享库
private static void preloadSharedLibraries() { Log.i(TAG, "Preloading shared libraries..."); System.loadLibrary("android"); System.loadLibrary("compiler_rt"); System.loadLibrary("jnigraphics"); }
5.4 加载prepareWebViewInZygote（不懂，预留）
6. socket
6.1 registerZygoteSocket
private static void registerZygoteSocket(String socketName) { if (sServerSocket == null) { int fileDesc; //fullSocketName=ANDROID_SOCKET_zygote,不过，我查了一下我们的代码，没有这个环境变量？？？？不知道为什么
final String fullSocketName = ANDROID_SOCKET_PREFIX + socketName;
try { String env = System.getenv(fullSocketName); //ANDROID_SOCKET_zygote fileDesc = Integer.parseInt(env); } catch (RuntimeException ex) { throw new RuntimeException(fullSocketName + " unset or invalid", ex); } try {
//创建一个socket本地服务的对象,这里的sServerSocket是一个静态属性，我们后面会用到 sServerSocket = new LocalServerSocket( createFileDescriptor(fileDesc)); } catch (IOException ex) { throw new RuntimeException( "Error binding to local socket '" + fileDesc + "'", ex); } } }
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
private static void registerZygoteSocket(String socketName) { if (sServerSocket == null) { int fileDesc; final String fullSocketName = ANDROID_SOCKET_PREFIX + socketName; try { String env = System.getenv(fullSocketName); //ANDROID_SOCKET_zygote fileDesc = Integer.parseInt(env); } catch (RuntimeException ex) { throw new RuntimeException(fullSocketName + " unset or invalid", ex); } try {
//这里的LocalServerSocket创建了一个对象，然后绑定socket，并listen
//createFileDescriptor是一个本地函数，通过JNI创建一个文件，并返回fd，如后面所示 sServerSocket = new LocalServerSocket( createFileDescriptor(fileDesc)); } catch (IOException ex) { throw new RuntimeException( "Error binding to local socket '" + fileDesc + "'", ex); } } }
6.2 com_android_internal_os_ZygoteInit.cpp
frameworks/base/core/jni/com_android_internal_os_ZygoteInit.cpp
static JNINativeMethod gMethods[] = { /* name, signature, funcPtr */ { "setreuid", "(II)I", (void*) com_android_internal_os_ZygoteInit_setreuid }, { "setregid", "(II)I", (void*) com_android_internal_os_ZygoteInit_setregid }, { "setpgid", "(II)I", (void *) com_android_internal_os_ZygoteInit_setpgid }, { "getpgid", "(I)I", (void *) com_android_internal_os_ZygoteInit_getpgid }, { "reopenStdio", "(Ljava/io/FileDescriptor;Ljava/io/FileDescriptor;" "Ljava/io/FileDescriptor;)V", (void *) com_android_internal_os_ZygoteInit_reopenStdio}, { "setCloseOnExec", "(Ljava/io/FileDescriptor;Z)V", (void *) com_android_internal_os_ZygoteInit_setCloseOnExec}, { "selectReadable", "([Ljava/io/FileDescriptor;)I", (void *) com_android_internal_os_ZygoteInit_selectReadable }, { "createFileDescriptor", "(I)Ljava/io/FileDescriptor;", (void *) com_android_internal_os_ZygoteInit_createFileDescriptor } /*这里就是上面所调用到的函数*/ };
static jobject com_android_internal_os_ZygoteInit_createFileDescriptor ( JNIEnv *env, jobject clazz, jint fd) { return jniCreateFileDescriptor(env, fd); //创建文件描述符 }
7. 启动SystemServer
这个函数是调用SystemServer.我就放入SystemServer的博客更合适一点
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
private static boolean startSystemServer(String abiList, String socketName) throws MethodAndArgsCaller, RuntimeException { long capabilities = posixCapabilitiesAsBits( OsConstants.CAP_BLOCK_SUSPEND, OsConstants.CAP_KILL, OsConstants.CAP_NET_ADMIN, OsConstants.CAP_NET_BIND_SERVICE, OsConstants.CAP_NET_BROADCAST, OsConstants.CAP_NET_RAW, OsConstants.CAP_SYS_MODULE, OsConstants.CAP_SYS_NICE, OsConstants.CAP_SYS_RESOURCE, OsConstants.CAP_SYS_TIME, OsConstants.CAP_SYS_TTY_CONFIG ); /* Hardcoded command line to start the system server */ String args[] = { "--setuid=1000", "--setgid=1000", "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1032,3001,3002,3003,3006,3007", "--capabilities=" + capabilities + "," + capabilities, "--runtime-init", "--nice-name=system_server", "com.android.server.SystemServer", }; ZygoteConnection.Arguments parsedArgs = null; int pid; try { parsedArgs = new ZygoteConnection.Arguments(args); ZygoteConnection.applyDebuggerSystemProperty(parsedArgs); ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs); /* Request to fork the system server process */
//通过fork创建子进程 pid = Zygote.forkSystemServer( parsedArgs.uid, parsedArgs.gid, parsedArgs.gids, parsedArgs.debugFlags, null, parsedArgs.permittedCapabilities, parsedArgs.effectiveCapabilities); } catch (IllegalArgumentException ex) { throw new RuntimeException(ex); } /* For child process */ if (pid == 0) { //从子进程跳入systemserver if (hasSecondZygote(abiList)) { waitForSecondaryZygote(socketName); } handleSystemServerProcess(parsedArgs); } return true; }
8. loop循环接收其他进程，并创建新进程
8.1 runSelectLoop
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
这里用到的socket的select模式，可以查看：Linux知识点
private static void runSelectLoop(String abiList) throws MethodAndArgsCaller { ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>(); ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>(); FileDescriptor[] fdArray = new FileDescriptor[4]; //新建一个数组 //拿到fd(也就是我们之前socket创建的)，并添加到容器 fds.add(sServerSocket.getFileDescriptor()); peers.add(null); int loopCount = GC_LOOP_COUNT; while (true) { int index; /* * Call gc() before we block in select(). * It's work that has to be done anyway, and it's better * to avoid making every child do it. It will also * madvise() any free memory as a side-effect. * * Don't call it every time, because walking the entire * heap is a lot of overhead to free a few hundred bytes. */ if (loopCount <= 0) { gc(); loopCount = GC_LOOP_COUNT; } else { loopCount--; } try {
//转换为数组 fdArray = fds.toArray(fdArray);
//调用本地函数去select，去监听数组fdArray,如后面所说 index = selectReadable(fdArray); } catch (IOException ex) { throw new RuntimeException("Error in select()", ex); } if (index < 0) { throw new RuntimeException("Error in select()"); //异常抛出 } else if (index == 0) {
//当select到了有可读数据之后，通过accept去监听
//这里的abiList是之前参数传进来的：--abi-list=armeabi-v71,armeabi
//新建以后再添加，监听 ZygoteConnection newPeer = acceptCommandPeer(abiList); peers.add(newPeer); fds.add(newPeer.getFileDescriptor()); } else { boolean done;
//当收到select以后，根据select索引，运行,具体查看章节9 done = peers.get(index).runOnce(); if (done) { peers.remove(index); fds.remove(index); } } } }
8.2 com_android_internal_os_ZygoteInit.cpp
frameworks/base/core/jni/com_android_internal_os_ZygoteInit.cpp
static JNINativeMethod gMethods[] = { /* name, signature, funcPtr */ { "setreuid", "(II)I", (void*) com_android_internal_os_ZygoteInit_setreuid }, { "setregid", "(II)I", (void*) com_android_internal_os_ZygoteInit_setregid }, { "setpgid", "(II)I", (void *) com_android_internal_os_ZygoteInit_setpgid }, { "getpgid", "(I)I", (void *) com_android_internal_os_ZygoteInit_getpgid }, { "reopenStdio", "(Ljava/io/FileDescriptor;Ljava/io/FileDescriptor;" "Ljava/io/FileDescriptor;)V", (void *) com_android_internal_os_ZygoteInit_reopenStdio}, { "setCloseOnExec", "(Ljava/io/FileDescriptor;Z)V", (void *) com_android_internal_os_ZygoteInit_setCloseOnExec}, { "selectReadable", "([Ljava/io/FileDescriptor;)I", (void *) com_android_internal_os_ZygoteInit_selectReadable }, //这一个是监听可读 { "createFileDescriptor", "(I)Ljava/io/FileDescriptor;", (void *) com_android_internal_os_ZygoteInit_createFileDescriptor } };
在这里关于select的用法和JNI的相关用法可以查看我的博客：
预留。。。
预留。。。
static jint com_android_internal_os_ZygoteInit_selectReadable ( JNIEnv *env, jobject clazz, jobjectArray fds) { if (fds == NULL) { jniThrowNullPointerException(env, "fds == null"); return -1; } jsize length = env->GetArrayLength(fds); fd_set fdset; if (env->ExceptionOccurred() != NULL) { return -1; } FD_ZERO(&fdset); int nfds = 0; for (jsize i = 0; i < length; i++) { jobject fdObj = env->GetObjectArrayElement(fds, i); if (env->ExceptionOccurred() != NULL) { return -1; } if (fdObj == NULL) { continue; } int fd = jniGetFDFromFileDescriptor(env, fdObj); if (env->ExceptionOccurred() != NULL) { return -1; } FD_SET(fd, &fdset); if (fd >= nfds) { nfds = fd + 1; } } int err; do { err = select (nfds, &fdset, NULL, NULL, NULL); //在这里监听 } while (err < 0 && errno == EINTR); if (err < 0) { jniThrowIOException(env, errno); return -1; } for (jsize i = 0; i < length; i++) { jobject fdObj = env->GetObjectArrayElement(fds, i); if (env->ExceptionOccurred() != NULL) { return -1; } if (fdObj == NULL) { continue; } int fd = jniGetFDFromFileDescriptor(env, fdObj); if (env->ExceptionOccurred() != NULL) { return -1; } if (FD_ISSET(fd, &fdset)) { return (jint)i; } } return -1; }
9. runOnce启动新进程（没有看的很懂，之后再分析）
frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java
从之前的
done = peers.get(index).runOnce();
然后查看peers类型
ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();
搜索ZygoteConnection可以找到
boolean runOnce() throws ZygoteInit.MethodAndArgsCaller { String args[]; Arguments parsedArgs = null; FileDescriptor[] descriptors; long startTime = SystemClock.elapsedRealtime(); try { args = readArgumentList(); descriptors = mSocket.getAncillaryFileDescriptors(); } catch (IOException ex) { Log.w(TAG, "IOException on command socket " + ex.getMessage()); closeSocket(); return true; } checkTime(startTime, "zygoteConnection.runOnce: readArgumentList"); if (args == null) { // EOF reached. closeSocket(); return true; } /** the stderr of the most recent request, if avail */ PrintStream newStderr = null; if (descriptors != null && descriptors.length >= 3) { newStderr = new PrintStream( new FileOutputStream(descriptors[2])); } int pid = -1; FileDescriptor childPipeFd = null; FileDescriptor serverPipeFd = null; try { parsedArgs = new Arguments(args); if (parsedArgs.abiListQuery) { return handleAbiListQuery(); } if (parsedArgs.permittedCapabilities != 0 || parsedArgs.effectiveCapabilities != 0) { throw new ZygoteSecurityException("Client may not specify capabilities: " + "permitted=0x" + Long.toHexString(parsedArgs.permittedCapabilities) + ", effective=0x" + Long.toHexString(parsedArgs.effectiveCapabilities)); } applyUidSecurityPolicy(parsedArgs, peer, peerSecurityContext); applyRlimitSecurityPolicy(parsedArgs, peer, peerSecurityContext); applyInvokeWithSecurityPolicy(parsedArgs, peer, peerSecurityContext); applyseInfoSecurityPolicy(parsedArgs, peer, peerSecurityContext); checkTime(startTime, "zygoteConnection.runOnce: apply security policies"); applyDebuggerSystemProperty(parsedArgs); applyInvokeWithSystemProperty(parsedArgs); checkTime(startTime, "zygoteConnection.runOnce: apply security policies"); int[][] rlimits = null; if (parsedArgs.rlimits != null) { rlimits = parsedArgs.rlimits.toArray(intArray2d); } if (parsedArgs.runtimeInit && parsedArgs.invokeWith != null) { FileDescriptor[] pipeFds = Os.pipe(); childPipeFd = pipeFds[1]; serverPipeFd = pipeFds[0]; ZygoteInit.setCloseOnExec(serverPipeFd, true); } /** * In order to avoid leaking descriptors to the Zygote child, * the native code must close the two Zygote socket descriptors * in the child process before it switches from Zygote-root to * the UID and privileges of the application being launched. * * In order to avoid "bad file descriptor" errors when the * two LocalSocket objects are closed, the Posix file * descriptors are released via a dup2() call which closes * the socket and substitutes an open descriptor to /dev/null. */ int [] fdsToClose = { -1, -1 }; FileDescriptor fd = mSocket.getFileDescriptor(); if (fd != null) { fdsToClose[0] = fd.getInt$(); } fd = ZygoteInit.getServerSocketFileDescriptor(); if (fd != null) { fdsToClose[1] = fd.getInt$(); } fd = null; checkTime(startTime, "zygoteConnection.runOnce: preForkAndSpecialize"); pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids, parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo, parsedArgs.niceName, fdsToClose, parsedArgs.instructionSet, parsedArgs.appDataDir); checkTime(startTime, "zygoteConnection.runOnce: postForkAndSpecialize"); } catch (IOException ex) { logAndPrintError(newStderr, "Exception creating pipe", ex); } catch (ErrnoException ex) { logAndPrintError(newStderr, "Exception creating pipe", ex); } catch (IllegalArgumentException ex) { logAndPrintError(newStderr, "Invalid zygote arguments", ex); } catch (ZygoteSecurityException ex) { logAndPrintError(newStderr, "Zygote security policy prevents request: ", ex); } try { if (pid == 0) { // in child IoUtils.closeQuietly(serverPipeFd); serverPipeFd = null; handleChildProc(parsedArgs, descriptors, childPipeFd, newStderr); // should never get here, the child is expected to either // throw ZygoteInit.MethodAndArgsCaller or exec(). return true; } else { // in parent...pid of < 0 means failure IoUtils.closeQuietly(childPipeFd); childPipeFd = null; return handleParentProc(pid, descriptors, serverPipeFd, parsedArgs); } } finally { IoUtils.closeQuietly(childPipeFd); IoUtils.closeQuietly(serverPipeFd); } }
