在Android中存在着C和Java两个完全不同的世界,前者直接建立在Linux的基础上,后者直接建立在JVM的基础上。zygote的中文名字为“受精卵”,这个名字很好的诠释了zygote进程的作用。作为java世界的孵化者,zygote本身是一个native程序,是由init根据init.rc文件中的配置项创建的。
@/system/core/rootdir/init.rc
- 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
关于init是如何解析和创建zygote进程的,这里不再赘述,不明的同学可以参考init进程【2】——解析配置文件一文。这里解析一下上面的第一行:service是rc脚本中的一种SECTION,zygote表示service的名字,/system/bin/app_process表示service的路径,-Xzygote /system/bin --zygote --start-system-server则表示传入的参数。
zygote的实现在app_main.cpp中:
@frameworks/base/cmds/app_process/app_main.cpp
- int main(int argc, char* const argv[])
- {
- //针对ARM平台的特殊逻辑
- #ifdef __arm__
- /*
- * b/7188322 - Temporarily revert to the compat memory layout
- * to avoid breaking third party apps.
- *
- * THIS WILL GO AWAY IN A FUTURE ANDROID RELEASE.
- *
- * http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7dbaa466
- * changes the kernel mapping from bottom up to top-down.
- * This breaks some programs which improperly embed
- * an out of date copy of Android's linker.
- */
- char value[PROPERTY_VALUE_MAX];
- property_get("ro.kernel.qemu", value, "");
- bool is_qemu = (strcmp(value, "1") == 0);
- if ((getenv("NO_ADDR_COMPAT_LAYOUT_FIXUP") == NULL) && !is_qemu) {
- int current = personality(0xFFFFFFFF);
- if ((current & ADDR_COMPAT_LAYOUT) == 0) {
- personality(current | ADDR_COMPAT_LAYOUT);
- setenv("NO_ADDR_COMPAT_LAYOUT_FIXUP", "1", 1);
- execv("/system/bin/app_process", argv);
- return -1;
- }
- }
- unsetenv("NO_ADDR_COMPAT_LAYOUT_FIXUP");
- #endif
- // These are global variables in ProcessState.cpp
- mArgC = argc;
- mArgV = argv;
- mArgLen = 0;
- for (int i=0; i<argc; i++) {
- mArgLen += strlen(argv[i]) + 1;
- }
- mArgLen--;
- AppRuntime runtime;
- const char* argv0 = argv[0];
- // Process command line arguments
- // ignore argv[0]
- argc--;
- argv++;
- // Everything up to '--' or first non '-' arg goes to the vm
- int i = runtime.addVmArguments(argc, argv);
- // Parse runtime arguments. Stop at first unrecognized option.
- bool zygote = false;
- bool startSystemServer = false;
- bool application = false;
- const char* parentDir = NULL;
- const char* niceName = NULL;
- const char* className = NULL;
- while (i < argc) {//根据传入的参数,初始化启动zygote所需的参数
- const char* arg = argv[i++];
- if (!parentDir) {
- parentDir = arg;
- } else if (strcmp(arg, "--zygote") == 0) {
- zygote = true;
- niceName = "zygote";
- } else if (strcmp(arg, "--start-system-server") == 0) {
- startSystemServer = true;
- } else if (strcmp(arg, "--application") == 0) {
- application = true;
- } else if (strncmp(arg, "--nice-name=", 12) == 0) {
- niceName = arg + 12;
- } else {
- className = arg;
- break;
- }
- }
- if (niceName && *niceName) {
- setArgv0(argv0, niceName);
- set_process_name(niceName);//设置本进程的名称为zygote,至此进程有app_process变为了zygote
- }
- runtime.mParentDir = parentDir;
- if (zygote) {//根据我们传入的参考,这里的zygote值为TRUE
- runtime.start("com.android.internal.os.ZygoteInit",
- startSystemServer ? "start-system-server" : "");
- } else if (className) {//可以看出除了zygote,RuntimeInit也是在这里启动的
- // Remainder of args get passed to startup class main()
- runtime.mClassName = className;
- runtime.mArgC = argc - i;
- runtime.mArgV = argv + i;
- runtime.start("com.android.internal.os.RuntimeInit",
- application ? "application" : "tool");
- } else {
- fprintf(stderr, "Error: no class name or --zygote supplied. ");
- app_usage();
- LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
- return 10;
- }
- }
通过对main()函数的分析,可以看出main()主要根据传入的参数初始化启动参数,具体的启动过程是由AppRuntime完成的。AppRuntime的声明和实现都在app_main.cpp中,它继承自AndroidRuntime,AppRuntime的实现如下:
- /*
- * Start the Android runtime. This involves starting the virtual machine
- * and calling the "static void main(String[] args)" method in the class
- * named by "className".
- *
- * Passes the main function two arguments, the class name and the specified
- * options string.
- */
- void AndroidRuntime::start(const char* className, const char* options)
- {
- ALOGD(" >>>>>> AndroidRuntime START %s <<<<<< ",
- className != NULL ? className : "(unknown)");
- /*
- * 'startSystemServer == true' means runtime is obsolete and not run from
- * init.rc anymore, so we print out the boot start event here.
- */
- if (strcmp(options, "start-system-server") == 0) {
- /* 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)));
- }
- //环境变量ANDROID_ROOT是否已经设置,如果未设置,则设置其值为"/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' ", kernelHack);
- /* start the virtual machine */
- JniInvocation jni_invocation;
- jni_invocation.Init(NULL);
- JNIEnv* env;
- if (startVm(&mJavaVM, &env) != 0) {//启动Java虚拟机
- return;
- }
- onVmCreated(env);//空函数
- /*
- * Register android functions.
- */
- if (startReg(env) < 0) {//注册Android JNI函数
- ALOGE("Unable to register all android natives ");
- 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.
- */
- jclass stringClass;
- jobjectArray strArray;
- jstring classNameStr;
- jstring optionsStr;
- stringClass = env->FindClass("java/lang/String");//JNI中调用java中的String类
- assert(stringClass != NULL);
- //创建包含2个元素的String数组,这里相当于Java中的String strArray[] = new String[2]
- strArray = env->NewObjectArray(2, stringClass, NULL);
- assert(strArray != NULL);
- classNameStr = env->NewStringUTF(className);//classNameStr的值为"com.android.internal.os.ZygoteInit"
- assert(classNameStr != NULL);
- env->SetObjectArrayElement(strArray, 0, classNameStr);
- optionsStr = env->NewStringUTF(options);//optionsStr的值为"start-system-server"
- env->SetObjectArrayElement(strArray, 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);//将"com.android.internal.os.ZygoteInit"中的"."替换成"/"供JNI调用
- jclass startClass = env->FindClass(slashClassName);
- if (startClass == NULL) {
- ALOGE("JavaVM unable to locate class '%s' ", slashClassName);
- /* keep going */
- } else {
- jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
- "([Ljava/lang/String;)V");//ZygoteInit类中的main()方法
- if (startMeth == NULL) {
- ALOGE("JavaVM unable to find main() in '%s' ", className);
- /* keep going */
- } else {
- env->CallStaticVoidMethod(startClass, startMeth, strArray);//通过JNI调用main()方法
- #if 0
- if (env->ExceptionCheck())
- threadExitUncaughtException(env);
- #endif
- }
- }
- free(slashClassName);
- //如果JVM退出。这两句代码一般来说执行不到
- ALOGD("Shutting down VM ");
- if (mJavaVM->DetachCurrentThread() != JNI_OK)
- ALOGW("Warning: unable to detach main thread ");
- if (mJavaVM->DestroyJavaVM() != 0)
- ALOGW("Warning: VM did not shut down cleanly ");
- }
- 启动JVM。
- 注册Android JNI函数。
- 调用ZygoteInit的main()方法。
创建Java虚拟机
- /* start the virtual machine */
- JniInvocation jni_invocation;
- jni_invocation.Init(NULL);
- JNIEnv* env;
- if (startVm(&mJavaVM, &env) != 0) {//启动Java虚拟机
- return;
- }
- onVmCreated(env);//空函数
- bool JniInvocation::Init(const char* library) {
- #ifdef HAVE_ANDROID_OS
- char default_library[PROPERTY_VALUE_MAX];
- property_get("persist.sys.dalvik.vm.lib", default_library, "libdvm.so");
- #else
- const char* default_library = "libdvm.so";
- #endif
- if (library == NULL) {
- library = default_library;
- }
- handle_ = dlopen(library, RTLD_NOW);
- if (handle_ == NULL) {
- ALOGE("Failed to dlopen %s: %s", library, dlerror());
- return false;
- }
- if (!FindSymbol(reinterpret_cast<void**>(&JNI_GetDefaultJavaVMInitArgs_),
- "JNI_GetDefaultJavaVMInitArgs")) {
- return false;
- }
- if (!FindSymbol(reinterpret_cast<void**>(&JNI_CreateJavaVM_),
- "JNI_CreateJavaVM")) {
- return false;
- }
- if (!FindSymbol(reinterpret_cast<void**>(&JNI_GetCreatedJavaVMs_),
- "JNI_GetCreatedJavaVMs")) {
- return false;
- }
- return true;
- }
在初始化完虚拟机环境后,接下来调用startVm()来创建虚拟机。
- /*
- * Start the Dalvik Virtual Machine.
- *
- * Various arguments, most determined by system properties, are passed in.
- * The "mOptions" vector is updated.
- *
- * Returns 0 on success.
- */
- int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv)
- {
- int result = -1;
- JavaVMInitArgs initArgs;
- JavaVMOption opt;
- char propBuf[PROPERTY_VALUE_MAX];
- char stackTraceFileBuf[PROPERTY_VALUE_MAX];
- char dexoptFlagsBuf[PROPERTY_VALUE_MAX];
- char enableAssertBuf[sizeof("-ea:")-1 + PROPERTY_VALUE_MAX];
- char jniOptsBuf[sizeof("-Xjniopts:")-1 + PROPERTY_VALUE_MAX];
- char heapstartsizeOptsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
- char heapsizeOptsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
- char heapgrowthlimitOptsBuf[sizeof("-XX:HeapGrowthLimit=")-1 + PROPERTY_VALUE_MAX];
- char heapminfreeOptsBuf[sizeof("-XX:HeapMinFree=")-1 + PROPERTY_VALUE_MAX];
- char heapmaxfreeOptsBuf[sizeof("-XX:HeapMaxFree=")-1 + PROPERTY_VALUE_MAX];
- char heaptargetutilizationOptsBuf[sizeof("-XX:HeapTargetUtilization=")-1 + PROPERTY_VALUE_MAX];
- char jitcodecachesizeOptsBuf[sizeof("-Xjitcodecachesize:")-1 + PROPERTY_VALUE_MAX];
- char extraOptsBuf[PROPERTY_VALUE_MAX];
- char* stackTraceFile = NULL;
- bool checkJni = false;
- bool checkDexSum = false;
- bool logStdio = false;
- enum {
- kEMDefault,
- kEMIntPortable,
- kEMIntFast,
- kEMJitCompiler,
- } executionMode = kEMDefault;
- property_get("dalvik.vm.checkjni", propBuf, "");
- if (strcmp(propBuf, "true") == 0) {
- checkJni = true;
- } else if (strcmp(propBuf, "false") != 0) {
- /* property is neither true nor false; fall back on kernel parameter */
- property_get("ro.kernel.android.checkjni", propBuf, "");
- if (propBuf[0] == '1') {
- checkJni = true;
- }
- }
- property_get("dalvik.vm.execution-mode", propBuf, "");
- if (strcmp(propBuf, "int:portable") == 0) {
- executionMode = kEMIntPortable;
- } else if (strcmp(propBuf, "int:fast") == 0) {
- executionMode = kEMIntFast;
- } else if (strcmp(propBuf, "int:jit") == 0) {
- executionMode = kEMJitCompiler;
- }
- property_get("dalvik.vm.stack-trace-file", stackTraceFileBuf, "");
- property_get("dalvik.vm.check-dex-sum", propBuf, "");
- if (strcmp(propBuf, "true") == 0) {
- checkDexSum = true;
- }
- property_get("log.redirect-stdio", propBuf, "");
- if (strcmp(propBuf, "true") == 0) {
- logStdio = true;
- }
- strcpy(enableAssertBuf, "-ea:");
- property_get("dalvik.vm.enableassertions", enableAssertBuf+4, "");
- strcpy(jniOptsBuf, "-Xjniopts:");
- property_get("dalvik.vm.jniopts", jniOptsBuf+10, "");
- /* route exit() to our handler */
- opt.extraInfo = (void*) runtime_exit;
- opt.optionString = "exit";
- mOptions.add(opt);
- /* route fprintf() to our handler */
- opt.extraInfo = (void*) runtime_vfprintf;
- opt.optionString = "vfprintf";
- mOptions.add(opt);
- /* register the framework-specific "is sensitive thread" hook */
- opt.extraInfo = (void*) runtime_isSensitiveThread;
- opt.optionString = "sensitiveThread";
- mOptions.add(opt);
- opt.extraInfo = NULL;
- /* enable verbose; standard options are { jni, gc, class } */
- //options[curOpt++].optionString = "-verbose:jni";
- opt.optionString = "-verbose:gc";
- mOptions.add(opt);
- //options[curOpt++].optionString = "-verbose:class";
- /*
- * The default starting and maximum size of the heap. Larger
- * values should be specified in a product property override.
- */
- strcpy(heapstartsizeOptsBuf, "-Xms");
- property_get("dalvik.vm.heapstartsize", heapstartsizeOptsBuf+4, "4m");
- opt.optionString = heapstartsizeOptsBuf;
- mOptions.add(opt);
- strcpy(heapsizeOptsBuf, "-Xmx");
- property_get("dalvik.vm.heapsize", heapsizeOptsBuf+4, "16m");
- opt.optionString = heapsizeOptsBuf;
- mOptions.add(opt);
- // Increase the main thread's interpreter stack size for bug 6315322.
- opt.optionString = "-XX:mainThreadStackSize=24K";
- mOptions.add(opt);
- // Set the max jit code cache size. Note: size of 0 will disable the JIT.
- strcpy(jitcodecachesizeOptsBuf, "-Xjitcodecachesize:");
- property_get("dalvik.vm.jit.codecachesize", jitcodecachesizeOptsBuf+19, NULL);
- if (jitcodecachesizeOptsBuf[19] != ' ') {
- opt.optionString = jitcodecachesizeOptsBuf;
- mOptions.add(opt);
- }
- strcpy(heapgrowthlimitOptsBuf, "-XX:HeapGrowthLimit=");
- property_get("dalvik.vm.heapgrowthlimit", heapgrowthlimitOptsBuf+20, "");
- if (heapgrowthlimitOptsBuf[20] != ' ') {
- opt.optionString = heapgrowthlimitOptsBuf;
- mOptions.add(opt);
- }
- strcpy(heapminfreeOptsBuf, "-XX:HeapMinFree=");
- property_get("dalvik.vm.heapminfree", heapminfreeOptsBuf+16, "");
- if (heapminfreeOptsBuf[16] != ' ') {
- opt.optionString = heapminfreeOptsBuf;
- mOptions.add(opt);
- }
- strcpy(heapmaxfreeOptsBuf, "-XX:HeapMaxFree=");
- property_get("dalvik.vm.heapmaxfree", heapmaxfreeOptsBuf+16, "");
- if (heapmaxfreeOptsBuf[16] != ' ') {
- opt.optionString = heapmaxfreeOptsBuf;
- mOptions.add(opt);
- }
- strcpy(heaptargetutilizationOptsBuf, "-XX:HeapTargetUtilization=");
- property_get("dalvik.vm.heaptargetutilization", heaptargetutilizationOptsBuf+26, "");
- if (heaptargetutilizationOptsBuf[26] != ' ') {
- opt.optionString = heaptargetutilizationOptsBuf;
- mOptions.add(opt);
- }
- property_get("ro.config.low_ram", propBuf, "");
- if (strcmp(propBuf, "true") == 0) {
- opt.optionString = "-XX:LowMemoryMode";
- mOptions.add(opt);
- }
- /*
- * Enable or disable dexopt features, such as bytecode verification and
- * calculation of register maps for precise GC.
- */
- property_get("dalvik.vm.dexopt-flags", dexoptFlagsBuf, "");
- if (dexoptFlagsBuf[0] != ' ') {
- const char* opc;
- const char* val;
- opc = strstr(dexoptFlagsBuf, "v="); /* verification */
- if (opc != NULL) {
- switch (*(opc+2)) {
- case 'n': val = "-Xverify:none"; break;
- case 'r': val = "-Xverify:remote"; break;
- case 'a': val = "-Xverify:all"; break;
- default: val = NULL; break;
- }
- if (val != NULL) {
- opt.optionString = val;
- mOptions.add(opt);
- }
- }
- opc = strstr(dexoptFlagsBuf, "o="); /* optimization */
- if (opc != NULL) {
- switch (*(opc+2)) {
- case 'n': val = "-Xdexopt:none"; break;
- case 'v': val = "-Xdexopt:verified"; break;
- case 'a': val = "-Xdexopt:all"; break;
- case 'f': val = "-Xdexopt:full"; break;
- default: val = NULL; break;
- }
- if (val != NULL) {
- opt.optionString = val;
- mOptions.add(opt);
- }
- }
- opc = strstr(dexoptFlagsBuf, "m=y"); /* register map */
- if (opc != NULL) {
- opt.optionString = "-Xgenregmap";
- mOptions.add(opt);
- /* turn on precise GC while we're at it */
- opt.optionString = "-Xgc:precise";
- mOptions.add(opt);
- }
- }
- /* enable debugging; set suspend=y to pause during VM init */
- /* use android ADB transport */
- opt.optionString =
- "-agentlib:jdwp=transport=dt_android_adb,suspend=n,server=y";
- mOptions.add(opt);
- ALOGD("CheckJNI is %s ", checkJni ? "ON" : "OFF");
- if (checkJni) {
- /* extended JNI checking */
- opt.optionString = "-Xcheck:jni";
- mOptions.add(opt);
- /* set a cap on JNI global references */
- opt.optionString = "-Xjnigreflimit:2000";
- mOptions.add(opt);
- /* with -Xcheck:jni, this provides a JNI function call trace */
- //opt.optionString = "-verbose:jni";
- //mOptions.add(opt);
- }
- char lockProfThresholdBuf[sizeof("-Xlockprofthreshold:") + sizeof(propBuf)];
- property_get("dalvik.vm.lockprof.threshold", propBuf, "");
- if (strlen(propBuf) > 0) {
- strcpy(lockProfThresholdBuf, "-Xlockprofthreshold:");
- strcat(lockProfThresholdBuf, propBuf);
- opt.optionString = lockProfThresholdBuf;
- mOptions.add(opt);
- }
- /* Force interpreter-only mode for selected opcodes. Eg "1-0a,3c,f1-ff" */
- char jitOpBuf[sizeof("-Xjitop:") + PROPERTY_VALUE_MAX];
- property_get("dalvik.vm.jit.op", propBuf, "");
- if (strlen(propBuf) > 0) {
- strcpy(jitOpBuf, "-Xjitop:");
- strcat(jitOpBuf, propBuf);
- opt.optionString = jitOpBuf;
- mOptions.add(opt);
- }
- /* Force interpreter-only mode for selected methods */
- char jitMethodBuf[sizeof("-Xjitmethod:") + PROPERTY_VALUE_MAX];
- property_get("dalvik.vm.jit.method", propBuf, "");
- if (strlen(propBuf) > 0) {
- strcpy(jitMethodBuf, "-Xjitmethod:");
- strcat(jitMethodBuf, propBuf);
- opt.optionString = jitMethodBuf;
- mOptions.add(opt);
- }
- if (executionMode == kEMIntPortable) {
- opt.optionString = "-Xint:portable";
- mOptions.add(opt);
- } else if (executionMode == kEMIntFast) {
- opt.optionString = "-Xint:fast";
- mOptions.add(opt);
- } else if (executionMode == kEMJitCompiler) {
- opt.optionString = "-Xint:jit";
- mOptions.add(opt);
- }
- if (checkDexSum) {
- /* perform additional DEX checksum tests */
- opt.optionString = "-Xcheckdexsum";
- mOptions.add(opt);
- }
- if (logStdio) {
- /* convert stdout/stderr to log messages */
- opt.optionString = "-Xlog-stdio";
- mOptions.add(opt);
- }
- if (enableAssertBuf[4] != ' ') {
- /* accept "all" to mean "all classes and packages" */
- if (strcmp(enableAssertBuf+4, "all") == 0)
- enableAssertBuf[3] = ' ';
- ALOGI("Assertions enabled: '%s' ", enableAssertBuf);
- opt.optionString = enableAssertBuf;
- mOptions.add(opt);
- } else {
- ALOGV("Assertions disabled ");
- }
- if (jniOptsBuf[10] != ' ') {
- ALOGI("JNI options: '%s' ", jniOptsBuf);
- opt.optionString = jniOptsBuf;
- mOptions.add(opt);
- }
- if (stackTraceFileBuf[0] != ' ') {
- static const char* stfOptName = "-Xstacktracefile:";
- stackTraceFile = (char*) malloc(strlen(stfOptName) +
- strlen(stackTraceFileBuf) +1);
- strcpy(stackTraceFile, stfOptName);
- strcat(stackTraceFile, stackTraceFileBuf);
- opt.optionString = stackTraceFile;
- mOptions.add(opt);
- }
- /* extra options; parse this late so it overrides others */
- property_get("dalvik.vm.extra-opts", extraOptsBuf, "");
- parseExtraOpts(extraOptsBuf);
- /* Set the properties for locale */
- {
- char langOption[sizeof("-Duser.language=") + 3];
- char regionOption[sizeof("-Duser.region=") + 3];
- strcpy(langOption, "-Duser.language=");
- strcpy(regionOption, "-Duser.region=");
- readLocale(langOption, regionOption);
- opt.extraInfo = NULL;
- opt.optionString = langOption;
- mOptions.add(opt);
- opt.optionString = regionOption;
- mOptions.add(opt);
- }
- /*
- * We don't have /tmp on the device, but we often have an SD card. Apps
- * shouldn't use this, but some test suites might want to exercise it.
- */
- opt.optionString = "-Djava.io.tmpdir=/sdcard";
- mOptions.add(opt);
- initArgs.version = JNI_VERSION_1_4;
- initArgs.options = mOptions.editArray();
- initArgs.nOptions = mOptions.size();
- initArgs.ignoreUnrecognized = JNI_FALSE;
- /*
- * Initialize the VM.
- *
- * The JavaVM* is essentially per-process, and the JNIEnv* is per-thread.
- * If this call succeeds, the VM is ready, and we can start issuing
- * JNI calls.
- */
- if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) < 0) {
- ALOGE("JNI_CreateJavaVM failed ");
- goto bail;
- }
- result = 0;
- bail:
- free(stackTraceFile);
- return result;
- }
- char propBuf[PROPERTY_VALUE_MAX];
- char stackTraceFileBuf[PROPERTY_VALUE_MAX];
- char dexoptFlagsBuf[PROPERTY_VALUE_MAX];
- char enableAssertBuf[sizeof("-ea:")-1 + PROPERTY_VALUE_MAX];
- char jniOptsBuf[sizeof("-Xjniopts:")-1 + PROPERTY_VALUE_MAX];
- char heapstartsizeOptsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
- char heapsizeOptsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
- char heapgrowthlimitOptsBuf[sizeof("-XX:HeapGrowthLimit=")-1 + PROPERTY_VALUE_MAX];
- char heapminfreeOptsBuf[sizeof("-XX:HeapMinFree=")-1 + PROPERTY_VALUE_MAX];
- char heapmaxfreeOptsBuf[sizeof("-XX:HeapMaxFree=")-1 + PROPERTY_VALUE_MAX];
- char heaptargetutilizationOptsBuf[sizeof("-XX:HeapTargetUtilization=")-1 + PROPERTY_VALUE_MAX];
- char jitcodecachesizeOptsBuf[sizeof("-Xjitcodecachesize:")-1 + PROPERTY_VALUE_MAX];
- /* System properties are *small* name value pairs managed by the
- ** property service. If your data doesn't fit in the provided
- ** space it is not appropriate for a system property.
- **
- ** WARNING: system/bionic/include/sys/system_properties.h also defines
- ** these, but with different names. (TODO: fix that)
- */
- #define PROPERTY_KEY_MAX PROP_NAME_MAX
- #define PROPERTY_VALUE_MAX PROP_VALUE_MAX
- [dalvik.vm.heapconcurrentstart]: [2097152]
- [dalvik.vm.heapgrowthlimit]: [96m]
- [dalvik.vm.heapidealfree]: [8388608]
- [dalvik.vm.heapsize]: [384m]
- [dalvik.vm.heapstartsize]: [8m]
- [dalvik.vm.heaputilization]: [0.25]
- [dalvik.vm.stack-trace-file]: [/data/anr/traces.txt]
- /*
- * Initialize the VM.
- *
- * The JavaVM* is essentially per-process, and the JNIEnv* is per-thread.
- * If this call succeeds, the VM is ready, and we can start issuing
- * JNI calls.
- */
- if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) < 0) {
- ALOGE("JNI_CreateJavaVM failed ");
- goto bail;
- }
注册JNI函数
- /*
- * Register android native functions with the VM.
- */
- /*static*/ int AndroidRuntime::startReg(JNIEnv* env)
- {
- /*
- * This hook causes all future threads created in this process to be
- * attached to the JavaVM. (This needs to go away in favor of JNI
- * Attach calls.)
- */
- <span style="white-space:pre"> </span>//设置Thread类的线程创建函数为javaCreateThreadEtc
- androidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc);
- ALOGV("--- registering native functions --- ");
- /*
- * Every "register" function calls one or more things that return
- * a local reference (e.g. FindClass). Because we haven't really
- * started the VM yet, they're all getting stored in the base frame
- * and never released. Use Push/Pop to manage the storage.
- */
- env->PushLocalFrame(200);
- if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
- env->PopLocalFrame(NULL);
- return -1;
- }
- env->PopLocalFrame(NULL);
- //createJavaThread("fubar", quickTest, (void*) "hello");
- return 0;
- }
- static int register_jni_procs(const RegJNIRec array[], size_t count, JNIEnv* env)
- {
- for (size_t i = 0; i < count; i++) {
- if (array[i].mProc(env) < 0) {
- #ifndef NDEBUG
- ALOGD("----------!!! %s failed to load ", array[i].mName);
- #endif
- return -1;
- }
- }
- return 0;
- }
- static const RegJNIRec gRegJNI[] = {
- REG_JNI(register_android_debug_JNITest),
- REG_JNI(register_com_android_internal_os_RuntimeInit),
- REG_JNI(register_android_os_SystemClock),
- REG_JNI(register_android_util_EventLog),
- REG_JNI(register_android_util_Log),
- REG_JNI(register_android_util_FloatMath),
- REG_JNI(register_android_text_format_Time),
- REG_JNI(register_android_content_AssetManager),
- REG_JNI(register_android_content_StringBlock),
- REG_JNI(register_android_content_XmlBlock),
- REG_JNI(register_android_emoji_EmojiFactory),
- REG_JNI(register_android_text_AndroidCharacter),
- REG_JNI(register_android_text_AndroidBidi),
- REG_JNI(register_android_view_InputDevice),
- REG_JNI(register_android_view_KeyCharacterMap),
- REG_JNI(register_android_os_Process),
- REG_JNI(register_android_os_SystemProperties),
- REG_JNI(register_android_os_Binder),
- REG_JNI(register_android_os_Parcel),
- REG_JNI(register_android_view_DisplayEventReceiver),
- REG_JNI(register_android_nio_utils),
- REG_JNI(register_android_graphics_Graphics),
- REG_JNI(register_android_view_GraphicBuffer),
- REG_JNI(register_android_view_GLES20DisplayList),
- REG_JNI(register_android_view_GLES20Canvas),
- REG_JNI(register_android_view_HardwareRenderer),
- REG_JNI(register_android_view_Surface),
- REG_JNI(register_android_view_SurfaceControl),
- REG_JNI(register_android_view_SurfaceSession),
- REG_JNI(register_android_view_TextureView),
- REG_JNI(register_com_google_android_gles_jni_EGLImpl),
- REG_JNI(register_com_google_android_gles_jni_GLImpl),
- REG_JNI(register_android_opengl_jni_EGL14),
- REG_JNI(register_android_opengl_jni_EGLExt),
- REG_JNI(register_android_opengl_jni_GLES10),
- REG_JNI(register_android_opengl_jni_GLES10Ext),
- REG_JNI(register_android_opengl_jni_GLES11),
- REG_JNI(register_android_opengl_jni_GLES11Ext),
- REG_JNI(register_android_opengl_jni_GLES20),
- REG_JNI(register_android_opengl_jni_GLES30),
- REG_JNI(register_android_graphics_Bitmap),
- REG_JNI(register_android_graphics_BitmapFactory),
- REG_JNI(register_android_graphics_BitmapRegionDecoder),
- REG_JNI(register_android_graphics_Camera),
- REG_JNI(register_android_graphics_CreateJavaOutputStreamAdaptor),
- REG_JNI(register_android_graphics_Canvas),
- REG_JNI(register_android_graphics_ColorFilter),
- REG_JNI(register_android_graphics_DrawFilter),
- REG_JNI(register_android_graphics_Interpolator),
- REG_JNI(register_android_graphics_LayerRasterizer),
- REG_JNI(register_android_graphics_MaskFilter),
- REG_JNI(register_android_graphics_Matrix),
- REG_JNI(register_android_graphics_Movie),
- REG_JNI(register_android_graphics_NinePatch),
- REG_JNI(register_android_graphics_Paint),
- REG_JNI(register_android_graphics_Path),
- REG_JNI(register_android_graphics_PathMeasure),
- REG_JNI(register_android_graphics_PathEffect),
- REG_JNI(register_android_graphics_Picture),
- REG_JNI(register_android_graphics_PorterDuff),
- REG_JNI(register_android_graphics_Rasterizer),
- REG_JNI(register_android_graphics_Region),
- REG_JNI(register_android_graphics_Shader),
- REG_JNI(register_android_graphics_SurfaceTexture),
- REG_JNI(register_android_graphics_Typeface),
- REG_JNI(register_android_graphics_Xfermode),
- REG_JNI(register_android_graphics_YuvImage),
- REG_JNI(register_android_graphics_pdf_PdfDocument),
- REG_JNI(register_android_database_CursorWindow),
- REG_JNI(register_android_database_SQLiteConnection),
- REG_JNI(register_android_database_SQLiteGlobal),
- REG_JNI(register_android_database_SQLiteDebug),
- REG_JNI(register_android_os_Debug),
- REG_JNI(register_android_os_FileObserver),
- REG_JNI(register_android_os_FileUtils),
- REG_JNI(register_android_os_MessageQueue),
- REG_JNI(register_android_os_SELinux),
- REG_JNI(register_android_os_Trace),
- REG_JNI(register_android_os_UEventObserver),
- REG_JNI(register_android_net_LocalSocketImpl),
- REG_JNI(register_android_net_NetworkUtils),
- REG_JNI(register_android_net_TrafficStats),
- REG_JNI(register_android_net_wifi_WifiNative),
- REG_JNI(register_android_os_MemoryFile),
- REG_JNI(register_com_android_internal_os_ZygoteInit),
- REG_JNI(register_android_hardware_Camera),
- REG_JNI(register_android_hardware_camera2_CameraMetadata),
- REG_JNI(register_android_hardware_SensorManager),
- REG_JNI(register_android_hardware_SerialPort),
- REG_JNI(register_android_hardware_UsbDevice),
- REG_JNI(register_android_hardware_UsbDeviceConnection),
- REG_JNI(register_android_hardware_UsbRequest),
- REG_JNI(register_android_media_AudioRecord),
- REG_JNI(register_android_media_AudioSystem),
- REG_JNI(register_android_media_AudioTrack),
- REG_JNI(register_android_media_JetPlayer),
- REG_JNI(register_android_media_RemoteDisplay),
- REG_JNI(register_android_media_ToneGenerator),
- REG_JNI(register_android_opengl_classes),
- REG_JNI(register_android_server_NetworkManagementSocketTagger),
- REG_JNI(register_android_server_Watchdog),
- REG_JNI(register_android_ddm_DdmHandleNativeHeap),
- REG_JNI(register_android_backup_BackupDataInput),
- REG_JNI(register_android_backup_BackupDataOutput),
- REG_JNI(register_android_backup_FileBackupHelperBase),
- REG_JNI(register_android_backup_BackupHelperDispatcher),
- REG_JNI(register_android_app_backup_FullBackup),
- REG_JNI(register_android_app_ActivityThread),
- REG_JNI(register_android_app_NativeActivity),
- REG_JNI(register_android_view_InputChannel),
- REG_JNI(register_android_view_InputEventReceiver),
- REG_JNI(register_android_view_InputEventSender),
- REG_JNI(register_android_view_InputQueue),
- REG_JNI(register_android_view_KeyEvent),
- REG_JNI(register_android_view_MotionEvent),
- REG_JNI(register_android_view_PointerIcon),
- REG_JNI(register_android_view_VelocityTracker),
- REG_JNI(register_android_content_res_ObbScanner),
- REG_JNI(register_android_content_res_Configuration),
- REG_JNI(register_android_animation_PropertyValuesHolder),
- REG_JNI(register_com_android_internal_content_NativeLibraryHelper),
- REG_JNI(register_com_android_internal_net_NetworkStatsFactory),
- };
- #ifdef NDEBUG
- #define REG_JNI(name) { name }
- struct RegJNIRec {
- int (*mProc)(JNIEnv*);
- };
- #else
- #define REG_JNI(name) { name, #name }
- struct RegJNIRec {
- int (*mProc)(JNIEnv*);
- const char* mName;
- };
- #endif
- { register_android_debug_JNITest, "register_android_debug_JNITest" }
- int register_android_debug_JNITest(JNIEnv* env)
- {
- return jniRegisterNativeMethods(env, "android/debug/JNITest",
- gMethods, NELEM(gMethods));
- }
到这里JNI注册就讲完了。
- env->CallStaticVoidMethod(startClass, startMeth, strArray);//通过JNI调用main()方法
- public static void main(String argv[]) {
- try {
- // Start profiling the zygote initialization.
- SamplingProfilerIntegration.start();//启动性能统计
- registerZygoteSocket();//注册zygote用的socket
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
- SystemClock.uptimeMillis());
- preload();//初始化,主要进行framework中一些类和资源的预加载
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
- SystemClock.uptimeMillis());
- // Finish profiling the zygote initialization.
- SamplingProfilerIntegration.writeZygoteSnapshot();//结束统计并生成结果文件
- // Do an initial gc to clean up after startup
- gc();//强制进行一次回收
- // Disable tracing so that forked processes do not inherit stale tracing tags from
- // Zygote.
- Trace.setTracingEnabled(false);
- // If requested, start system server directly from Zygote
- if (argv.length != 2) {
- throw new RuntimeException(argv[0] + USAGE_STRING);
- }
- if (argv[1].equals("start-system-server")) {
- startSystemServer();//启动system_server进程
- } else if (!argv[1].equals("")) {
- throw new RuntimeException(argv[0] + USAGE_STRING);
- }
- Log.i(TAG, "Accepting command socket connections");
- runSelectLoop();//变成守护进程,接收socket信息进行处理
- closeServerSocket();
- } catch (MethodAndArgsCaller caller) {
- caller.run();
- } catch (RuntimeException ex) {
- Log.e(TAG, "Zygote died with exception", ex);
- closeServerSocket();
- throw ex;
- }
- }
- 注册Zygote用的socket
- 类和资源的预加载
- 启动system_server进程
- 进入一个死循环,等待接收和处理socket事件
registerZygoteSocket()方法
- /**
- * Registers a server socket for zygote command connections
- *
- * @throws RuntimeException when open fails
- */
- private static void registerZygoteSocket() {
- if (sServerSocket == null) {
- int fileDesc;
- try {
- String env = System.getenv(ANDROID_SOCKET_ENV);//从环境变量中获取socket的fd
- fileDesc = Integer.parseInt(env);
- } catch (RuntimeException ex) {
- throw new RuntimeException(
- ANDROID_SOCKET_ENV + " unset or invalid", ex);
- }
- try {
- sServerSocket = new LocalServerSocket(
- createFileDescriptor(fileDesc));
- } catch (IOException ex) {
- throw new RuntimeException(
- "Error binding to local socket '" + fileDesc + "'", ex);
- }
- }
- }
在Zygote中通过preload()方法完成类和资源的加载,它的实现如下:
- static void preload() {
- preloadClasses();//加载类
- preloadResources();//加载资源
- preloadOpenGL();//加载OpenGL
- }
先看一下preloadClasses():
- /**
- * Performs Zygote process initialization. Loads and initializes
- * commonly used classes.
- *
- * Most classes only cause a few hundred bytes to be allocated, but
- * a few will allocate a dozen Kbytes (in one case, 500+K).
- */
- private static void preloadClasses() {
- final VMRuntime runtime = VMRuntime.getRuntime();
- InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream(
- PRELOADED_CLASSES);//加载preloaded-classes这个文件中定义的需要预加载的类
- if (is == null) {
- Log.e(TAG, "Couldn't find " + PRELOADED_CLASSES + ".");
- } else {
- 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) {
- // 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);//以反射的方式加载类
- 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 (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);
- }
- }
- }
preloadClasses()的实现很简单,这里说一下preloaded-classes文件:
- # Classes which are preloaded by com.android.internal.os.ZygoteInit.
- # Automatically generated by frameworks/base/tools/preload/WritePreloadedClassFile.java.
- # MIN_LOAD_TIME_MICROS=1250
- # MIN_PROCESSES=10
- android.R$styleable
- android.accounts.Account
- android.accounts.Account$1
- android.accounts.AccountManager
- android.accounts.AccountManager$12
- android.accounts.AccountManager$13
- android.accounts.AccountManager$6
- android.accounts.AccountManager$AmsTask
- android.accounts.AccountManager$AmsTask$1
- android.accounts.AccountManager$AmsTask$Response
在Android4.4的源代码中有2782行,也就说这里在系统启动时需要预加载两千多个类,而这仅仅是源代码,在手机厂商的代码中,需要进行预加载的类的数量将会超过这个数。preloaded-classes文件时由WritePreloadedClassFile类生成的。WritePreloadedClassFile将某个类加入预加载文件preloaded-classes中的条件时:该类被不少于10个进程使用,并且家中该类好使超过1250微秒。WritePreloadedClassFile里面的实现非常简单,感兴趣的读者可以自行阅读。
- /**
- * Preload any class that take longer to load than MIN_LOAD_TIME_MICROS us.
- */
- static final int MIN_LOAD_TIME_MICROS = 1250;
- /**
- * Preload any class that was loaded by at least MIN_PROCESSES processes.
- */
- static final int MIN_PROCESSES = 10;
这里我简单估算了一下,在Android4.4中预加载这些类需要4秒钟作用,这对于系统启动来说是一个比较长的时间,因此在进行系统启动速度的优化时,这里可以作为一个优化大点。
在看preloadClass的代码时有些读者看的setEffectiveUser的几句代码不明白什么意思:
- private static void preloadClasses() {
- ......
- // Drop root perms while running static initializers.
- setEffectiveGroup(UNPRIVILEGED_GID);
- setEffectiveUser(UNPRIVILEGED_UID);
- ......
- } finally {
- ......
- // Bring back root. We'll need it later.
- setEffectiveUser(ROOT_UID);
- setEffectiveGroup(ROOT_GID);
- }
- }
- }
以setEffectiveUser为例看一下它的实现:
- /**
- * Sets effective user ID.
- */
- private static void setEffectiveUser(int uid) {
- int errno = setreuid(ROOT_UID, uid);
- if (errno != 0) {
- Log.e(TAG, "setreuid() failed. errno: " + errno);
- }
- }
- /**
- * The Linux syscall "setreuid()"
- * @param ruid real uid
- * @param euid effective uid
- * @return 0 on success, non-zero errno on fail
- */
- static native int setreuid(int ruid, int euid);
可以看出这里setEffectiveUser这几句的意思是:在类加载之前临时降低euid(真实用户ID)权限,加载完成后恢复。关于Linux各种userid的说明如下:
有效用户ID
有效用户ID(Effective UID,即EUID)与有效用户组ID(Effective Group ID,即EGID)在创建与访问文件的时候发挥作用;具体来说,创建文件时,系统内核将根据创建文件的进程的EUID与EGID设定文件的所有者/组属性,而在访问文件时,内核亦根据访问进程的EUID与EGID决定其能否访问文件。
真实用户ID
真实用户ID(Real UID,即RUID)与真实用户组ID(Real GID,即RGID)用于辨识进程的真正所有者,且会影响到进程发送信号的权限。没有超级用户权限的进程仅在其RUID与目标进程的RUID相匹配时才能向目标进程发送信号,例如在父子进程间,子进程从父进程处继承了认证信息,使得父子进程间可以互相发送信号。
暂存用户ID
暂存用户ID(Saved UID,即SUID)于以提升权限运行的进程暂时需要做一些不需特权的操作时使用,这种情况下进程会暂时将自己的有效用户ID从特权用户(常为root)对应的UID变为某个非特权用户对应的UID,而后将原有的特权用户UID复制为SUID暂存;之后当进程完成不需特权的操作后,进程使用SUID的值重置EUID以重新获得特权。在这里需要说明的是,无特权进程的EUID值只能设为与RUID、SUID与EUID(也即不改变)之一相同的值。
文件系统用户ID
文件系统用户ID(File System UID,即FSUID)在Linux中使用,且只用于对文件系统的访问权限控制,在没有明确设定的情况下与EUID相同(若FSUID为root的UID,则SUID、RUID与EUID必至少有一亦为root的UID),且EUID改变也会影响到FSUID。设立FSUID是为了允许程序(如NFS服务器)在不需获取向给定UID账户发送信号的情况下以给定UID的权限来限定自己的文件系统权限。
这段代码转自http://zh.wikipedia.org/wiki/%E7%94%A8%E6%88%B7ID
那这里这样做的用意何在?我猜这里是为了保证预加载的类是所有的用户都是可用的。
预加载资源的代码如下:
- /**
- * Load in commonly used resources, so they can be shared across
- * processes.
- *
- * These tend to be a few Kbytes, but are frequently in the 20-40K
- * range, and occasionally even larger.
- */
- 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);//预加载Drawable
- 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);//预加载Color
- 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();
- }
- }
preloadResources的加载过程又分为加载Drawable和加载Color。
除了加载类和资源,还会加载OpenGL的一些东西:
- private static void preloadOpenGL() {
- if (!SystemProperties.getBoolean(PROPERTY_DISABLE_OPENGL_PRELOADING, false)) {
- EGL14.eglGetDisplay(EGL14.EGL_DEFAULT_DISPLAY);
- }
- }
在创建socket和资源加载前后有这么两句:
- // Start profiling the zygote initialization.
- SamplingProfilerIntegration.start();//启动性能统计
- registerZygoteSocket();//注册zygote用的socket
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
- SystemClock.uptimeMillis());
- preload();//初始化,主要进行framework中一些类和资源的预加载
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
- SystemClock.uptimeMillis());
- // Finish profiling the zygote initialization.
- SamplingProfilerIntegration.writeZygoteSnapshot();//结束统计并生成结果文件
所以,这里SamplingProfilerIntegration统计的是创建socket和类及资源初始化的时间。
启动system_server
- /**
- * Prepare the arguments and fork for the system server process.
- */
- private static boolean startSystemServer()
- throws MethodAndArgsCaller, RuntimeException {
- long capabilities = posixCapabilitiesAsBits(
- 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 */
- pid = Zygote.forkSystemServer(//以fork的方式创建system_server进程
- 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) {//pid==0说明在子进程中,父进程为Zygote
- handleSystemServerProcess(parsedArgs);
- }
- return true;
- }
这里前面的一大段代码主要是在为fork准备参数parsedArgs,然后Zygote会forkSystemServer来创建system_server,forkSystemServer()方法最终会调用Linux中的fork()。
runSelectLoop()方法
在创建system_server后,Zygote调用runSelectLoop()进入到一个死循环中:
- /**
- * Runs the zygote process's select loop. Accepts new connections as
- * they happen, and reads commands from connections one spawn-request's
- * worth at a time.
- *
- * @throws MethodAndArgsCaller in a child process when a main() should
- * be executed.
- */
- private static void runSelectLoop() throws MethodAndArgsCaller {
- ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>();
- ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();
- FileDescriptor[] fdArray = new FileDescriptor[4];
- fds.add(sServerSocket.getFileDescriptor());//registerZygoteSocket中创建的socket的描述符
- peers.add(null);
- int loopCount = GC_LOOP_COUNT;
- while (true) {//死循环
- int index;//selectReadable方法监控的句柄的下标(fdArray中的下标)
- /*
- * 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) {//Zygote每循环GC_LOOP_COUNT(这里的值是10)次就会进行一次内存回收
- gc();
- loopCount = GC_LOOP_COUNT;
- } else {
- loopCount--;
- }
- try {
- fdArray = fds.toArray(fdArray);
- index = selectReadable(fdArray);//内部由select()实现,在没有客户端事件时会堵塞
- } catch (IOException ex) {
- throw new RuntimeException("Error in select()", ex);
- }
- if (index < 0) {
- throw new RuntimeException("Error in select()");
- } else if (index == 0) {//index==0表示selcet接收到的是Zygote的socket的事件
- ZygoteConnection newPeer = acceptCommandPeer();
- peers.add(newPeer);
- fds.add(newPeer.getFileDesciptor());
- } else {//调用ZygoteConnection对象的runOnce方法,ZygoteConnection是在index == 0时被添加到peers的
- boolean done;
- done = peers.get(index).runOnce();
- if (done) {
- peers.remove(index);
- fds.remove(index);
- }
- }
- }
- }
下面是selcetReadable方法的代码:
- /**
- * Invokes select() on the provider array of file descriptors (selecting
- * for readability only). Array elements of null are ignored.
- *
- * @param fds non-null; array of readable file descriptors
- * @return index of descriptor that is now readable or -1 for empty array.
- * @throws IOException if an error occurs
- */
- static native int selectReadable(FileDescriptor[] fds) throws IOException;
selectReadable的native实现在com_android_internal_os_ZygoteInit.cpp中。
Zygote接收到socket客户端的链接后会将其(客户端Socket)保存到一个ZygoteConnection对象中,然后保存到peers
- /**
- * Waits for and accepts a single command connection. Throws
- * RuntimeException on failure.
- */
- private static ZygoteConnection acceptCommandPeer() {
- try {
- return new ZygoteConnection(sServerSocket.accept());
- } catch (IOException ex) {
- throw new RuntimeException(
- "IOException during accept()", ex);
- }
- }
最后,客户端的请求会有ZygoteConnection的runOnce来处理。