Zygote 是Android第一个应用进程，它由init程序解析import /init.${ro.zygote}.rc 所启动。
ro.zygote32.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
writepid /dev/cpuset/foreground/tasks
看到它的启动由app_process 执行文件启动，接下来分析app_process源码：frameworks/base/cmds/app_process/app_main.cpp，直接看其的main函数
Vector args;
if (!className.isEmpty()) {
args.add(application ? String8("application") : String8("tool"));
runtime.setClassNameAndArgs(className, argc - i, argv + i);
} else {
// We're in zygote mode.
maybeCreateDalvikCache();
if (startSystemServer) {
args.add(String8("start-system-server"));
}
char prop[PROP_VALUE_MAX];
if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
ABI_LIST_PROPERTY);
return 11;
}
String8 abiFlag("--abi-list=");
abiFlag.append(prop);
args.add(abiFlag);
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (; i < argc; ++i) {
args.add(String8(argv[i]));
}
}
if (!niceName.isEmpty()) {
runtime.setArgv0(niceName.string());
set_process_name(niceName.string());
}
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
} else if (className) {
runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
bool debug = false;
if (debug) {
ALOGD("app_process pid:%d, ppid:%d.", getpid(), getppid());
String8 cmd;
for (int i = 0; i < argc; i++) {
cmd.append(argv[i]);
if (i < argc -1) {
cmd.append(" ");
}
}
ALOGD("app_process %s.", cmd.string());
FILE* processF = popen("ps >> /data/system/app_process.txt;", "r");
if (processF) {
pclose(processF);
}
}
} 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;
}
通过解析启动参数，判断是否启动Zygote程序自身或者其他进程，是否需要启动SystemServer进程。Ps: else if 条件分支处系我加的日志。
无论启动的是否为zygote，都执行了Runtime.start函数(frameworks/base/core/jni/AndroidRuntime.cpp 中的start函数)，该函数的核心是启动虚拟机实例，并注册androidAPI基础类中的所以native函数，并且反射ZygoteInit类的main函数。
/* start the virtual machine */
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
if (startVm(&mJavaVM, &env, zygote) != 0) {
return;
}
onVmCreated(env);
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}
现在看启动虚拟机实例的startVM函数
int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote)
{
JavaVMInitArgs initArgs;
char propBuf[PROPERTY_VALUE_MAX];
char stackTraceFileBuf[sizeof("-Xstacktracefile:")-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 usejitOptsBuf[sizeof("-Xusejit:")-1 + PROPERTY_VALUE_MAX];
char jitcodecachesizeOptsBuf[sizeof("-Xjitcodecachesize:")-1 + PROPERTY_VALUE_MAX];
char jitthresholdOptsBuf[sizeof("-Xjitthreshold:")-1 + PROPERTY_VALUE_MAX];
char gctypeOptsBuf[sizeof("-Xgc:")-1 + PROPERTY_VALUE_MAX];
char backgroundgcOptsBuf[sizeof("-XX:BackgroundGC=")-1 + PROPERTY_VALUE_MAX];
char heaptargetutilizationOptsBuf[sizeof("-XX:HeapTargetUtilization=")-1 + PROPERTY_VALUE_MAX];
char cachePruneBuf[sizeof("-Xzygote-max-boot-retry=")-1 + PROPERTY_VALUE_MAX];
char dex2oatXmsImageFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
char dex2oatXmxImageFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
char dex2oatXmsFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
char dex2oatXmxFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
char dex2oatCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
char dex2oatImageCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
char dex2oatThreadsBuf[sizeof("-j")-1 + PROPERTY_VALUE_MAX];
char dex2oatThreadsImageBuf[sizeof("-j")-1 + PROPERTY_VALUE_MAX];
char dex2oat_isa_variant_key[PROPERTY_KEY_MAX];
char dex2oat_isa_variant[sizeof("--instruction-set-variant=") -1 + PROPERTY_VALUE_MAX];
char dex2oat_isa_features_key[PROPERTY_KEY_MAX];
char dex2oat_isa_features[sizeof("--instruction-set-features=") -1 + PROPERTY_VALUE_MAX];
char dex2oatFlagsBuf[PROPERTY_VALUE_MAX];
char dex2oatImageFlagsBuf[PROPERTY_VALUE_MAX];
char extraOptsBuf[PROPERTY_VALUE_MAX];
char voldDecryptBuf[PROPERTY_VALUE_MAX];
enum {
kEMDefault,
kEMIntPortable,
kEMIntFast,
kEMJitCompiler,
} executionMode = kEMDefault;
char profilePeriod[sizeof("-Xprofile-period:")-1 + PROPERTY_VALUE_MAX];
char profileDuration[sizeof("-Xprofile-duration:")-1 + PROPERTY_VALUE_MAX];
char profileInterval[sizeof("-Xprofile-interval:")-1 + PROPERTY_VALUE_MAX];
char profileBackoff[sizeof("-Xprofile-backoff:")-1 + PROPERTY_VALUE_MAX];
char profileTopKThreshold[sizeof("-Xprofile-top-k-threshold:")-1 + PROPERTY_VALUE_MAX];
char profileTopKChangeThreshold[sizeof("-Xprofile-top-k-change-threshold:")-1 +
PROPERTY_VALUE_MAX];
char profileType[sizeof("-Xprofile-type:")-1 + PROPERTY_VALUE_MAX];
char profileMaxStackDepth[sizeof("-Xprofile-max-stack-depth:")-1 + PROPERTY_VALUE_MAX];
char localeOption[sizeof("-Duser.locale=") + PROPERTY_VALUE_MAX];
char lockProfThresholdBuf[sizeof("-Xlockprofthreshold:")-1 + PROPERTY_VALUE_MAX];
char nativeBridgeLibrary[sizeof("-XX:NativeBridge=") + PROPERTY_VALUE_MAX];
char cpuAbiListBuf[sizeof("--cpu-abilist=") + PROPERTY_VALUE_MAX];
char methodTraceFileBuf[sizeof("-Xmethod-trace-file:") + PROPERTY_VALUE_MAX];
char methodTraceFileSizeBuf[sizeof("-Xmethod-trace-file-size:") + PROPERTY_VALUE_MAX];
char fingerprintBuf[sizeof("-Xfingerprint:") + PROPERTY_VALUE_MAX];
bool checkJni = false;
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;
}
}
ALOGD("CheckJNI is %s\n", checkJni ? "ON" : "OFF");
if (checkJni) {
/* extended JNI checking */
addOption("-Xcheck:jni");
/* with -Xcheck:jni, this provides a JNI function call trace */
//addOption("-verbose:jni");
}
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;
}
parseRuntimeOption("dalvik.vm.stack-trace-file", stackTraceFileBuf, "-Xstacktracefile:");
strcpy(jniOptsBuf, "-Xjniopts:");
if (parseRuntimeOption("dalvik.vm.jniopts", jniOptsBuf, "-Xjniopts:")) {
ALOGI("JNI options: '%s'\n", jniOptsBuf);
}
/* route exit() to our handler */
addOption("exit", (void*) runtime_exit);
/* route fprintf() to our handler */
addOption("vfprintf", (void*) runtime_vfprintf);
/* register the framework-specific "is sensitive thread" hook */
addOption("sensitiveThread", (void*) runtime_isSensitiveThread);
/* enable verbose; standard options are { jni, gc, class } */
//addOption("-verbose:jni");
addOption("-verbose:gc");
//addOption("-verbose:class");
/*
* The default starting and maximum size of the heap. Larger
* values should be specified in a product property override.
*/
parseRuntimeOption("dalvik.vm.heapstartsize", heapstartsizeOptsBuf, "-Xms", "4m");
parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m");
parseRuntimeOption("dalvik.vm.heapgrowthlimit", heapgrowthlimitOptsBuf, "-XX:HeapGrowthLimit=");
parseRuntimeOption("dalvik.vm.heapminfree", heapminfreeOptsBuf, "-XX:HeapMinFree=");
parseRuntimeOption("dalvik.vm.heapmaxfree", heapmaxfreeOptsBuf, "-XX:HeapMaxFree=");
parseRuntimeOption("dalvik.vm.heaptargetutilization",
heaptargetutilizationOptsBuf,
"-XX:HeapTargetUtilization=");
/*
* JIT related options.
*/
parseRuntimeOption("dalvik.vm.usejit", usejitOptsBuf, "-Xusejit:");
parseRuntimeOption("dalvik.vm.jitcodecachesize", jitcodecachesizeOptsBuf, "-Xjitcodecachesize:");
parseRuntimeOption("dalvik.vm.jitthreshold", jitthresholdOptsBuf, "-Xjitthreshold:");
property_get("ro.config.low_ram", propBuf, "");
if (strcmp(propBuf, "true") == 0) {
addOption("-XX:LowMemoryMode");
}
parseRuntimeOption("dalvik.vm.gctype", gctypeOptsBuf, "-Xgc:");
parseRuntimeOption("dalvik.vm.backgroundgctype", backgroundgcOptsBuf, "-XX:BackgroundGC=");
/*
* Enable debugging only for apps forked from zygote.
* Set suspend=y to pause during VM init and use android ADB transport.
*/
if (zygote) {
addOption("-agentlib:jdwp=transport=dt_android_adb,suspend=n,server=y");
}
parseRuntimeOption("dalvik.vm.lockprof.threshold",
lockProfThresholdBuf,
"-Xlockprofthreshold:");
if (executionMode == kEMIntPortable) {
addOption("-Xint:portable");
} else if (executionMode == kEMIntFast) {
addOption("-Xint:fast");
} else if (executionMode == kEMJitCompiler) {
addOption("-Xint:jit");
}
// If we are booting without the real /data, don't spend time compiling.
property_get("vold.decrypt", voldDecryptBuf, "");
bool skip_compilation = ((strcmp(voldDecryptBuf, "trigger_restart_min_framework") == 0) ||
(strcmp(voldDecryptBuf, "1") == 0));
// Extra options for boot.art/boot.oat image generation.
parseCompilerRuntimeOption("dalvik.vm.image-dex2oat-Xms", dex2oatXmsImageFlagsBuf,
"-Xms", "-Ximage-compiler-option");
parseCompilerRuntimeOption("dalvik.vm.image-dex2oat-Xmx", dex2oatXmxImageFlagsBuf,
"-Xmx", "-Ximage-compiler-option");
if (skip_compilation) {
addOption("-Ximage-compiler-option");
addOption("--compiler-filter=verify-none");
} else {
parseCompilerOption("dalvik.vm.image-dex2oat-filter", dex2oatImageCompilerFilterBuf,
"--compiler-filter=", "-Ximage-compiler-option");
}
// Make sure there is a preloaded-classes file.
if (!hasFile("/system/etc/preloaded-classes")) {
ALOGE("Missing preloaded-classes file, /system/etc/preloaded-classes not found: %s\n",
strerror(errno));
return -1;
}
addOption("-Ximage-compiler-option");
addOption("--image-classes=/system/etc/preloaded-classes");
// If there is a compiled-classes file, push it.
if (hasFile("/system/etc/compiled-classes")) {
addOption("-Ximage-compiler-option");
addOption("--compiled-classes=/system/etc/compiled-classes");
}
property_get("dalvik.vm.image-dex2oat-flags", dex2oatImageFlagsBuf, "");
parseExtraOpts(dex2oatImageFlagsBuf, "-Ximage-compiler-option");
// Extra options for DexClassLoader.
parseCompilerRuntimeOption("dalvik.vm.dex2oat-Xms", dex2oatXmsFlagsBuf,
"-Xms", "-Xcompiler-option");
parseCompilerRuntimeOption("dalvik.vm.dex2oat-Xmx", dex2oatXmxFlagsBuf,
"-Xmx", "-Xcompiler-option");
if (skip_compilation) {
addOption("-Xcompiler-option");
addOption("--compiler-filter=verify-none");
// We skip compilation when a minimal runtime is brought up for decryption. In that case
// /data is temporarily backed by a tmpfs, which is usually small.
// If the system image contains prebuilts, they will be relocated into the tmpfs. In this
// specific situation it is acceptable to *not* relocate and run out of the prebuilts
// directly instead.
addOption("--runtime-arg");
addOption("-Xnorelocate");
} else {
parseCompilerOption("dalvik.vm.dex2oat-filter", dex2oatCompilerFilterBuf,
"--compiler-filter=", "-Xcompiler-option");
}
parseCompilerOption("dalvik.vm.dex2oat-threads", dex2oatThreadsBuf, "-j", "-Xcompiler-option");
parseCompilerOption("dalvik.vm.image-dex2oat-threads", dex2oatThreadsImageBuf, "-j",
"-Ximage-compiler-option");
// The runtime will compile a boot image, when necessary, not using installd. Thus, we need to
// pass the instruction-set-features/variant as an image-compiler-option.
// TODO: Find a better way for the instruction-set.
#if defined(__arm__)
constexpr const char* instruction_set = "arm";
#elif defined(__aarch64__)
constexpr const char* instruction_set = "arm64";
#elif defined(__mips__) && !defined(__LP64__)
constexpr const char* instruction_set = "mips";
#elif defined(__mips__) && defined(__LP64__)
constexpr const char* instruction_set = "mips64";
#elif defined(__i386__)
constexpr const char* instruction_set = "x86";
#elif defined(__x86_64__)
constexpr const char* instruction_set = "x86_64";
#else
constexpr const char* instruction_set = "unknown";
#endif
// Note: it is OK to reuse the buffer, as the values are exactly the same between
// * compiler-option, used for runtime compilation (DexClassLoader)
// * image-compiler-option, used for boot-image compilation on device
// Copy the variant.
sprintf(dex2oat_isa_variant_key, "dalvik.vm.isa.%s.variant", instruction_set);
parseCompilerOption(dex2oat_isa_variant_key, dex2oat_isa_variant,
"--instruction-set-variant=", "-Ximage-compiler-option");
parseCompilerOption(dex2oat_isa_variant_key, dex2oat_isa_variant,
"--instruction-set-variant=", "-Xcompiler-option");
// Copy the features.
sprintf(dex2oat_isa_features_key, "dalvik.vm.isa.%s.features", instruction_set);
parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features,
"--instruction-set-features=", "-Ximage-compiler-option");
parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features,
"--instruction-set-features=", "-Xcompiler-option");
property_get("dalvik.vm.dex2oat-flags", dex2oatFlagsBuf, "");
parseExtraOpts(dex2oatFlagsBuf, "-Xcompiler-option");
/* extra options; parse this late so it overrides others */
property_get("dalvik.vm.extra-opts", extraOptsBuf, "");
parseExtraOpts(extraOptsBuf, NULL);
/* Set the properties for locale */
{
strcpy(localeOption, "-Duser.locale=");
const std::string locale = readLocale();
strncat(localeOption, locale.c_str(), PROPERTY_VALUE_MAX);
addOption(localeOption);
}
/*
* Set profiler options
*/
// Whether or not the profiler should be enabled.
property_get("dalvik.vm.profiler", propBuf, "0");
if (propBuf[0] == '1') {
addOption("-Xenable-profiler");
}
// Whether the profile should start upon app startup or be delayed by some random offset
// (in seconds) that is bound between 0 and a fixed value.
property_get("dalvik.vm.profile.start-immed", propBuf, "0");
if (propBuf[0] == '1') {
addOption("-Xprofile-start-immediately");
}
// Number of seconds during profile runs.
parseRuntimeOption("dalvik.vm.profile.period-secs", profilePeriod, "-Xprofile-period:");
// Length of each profile run (seconds).
parseRuntimeOption("dalvik.vm.profile.duration-secs",
profileDuration,
"-Xprofile-duration:");
// Polling interval during profile run (microseconds).
parseRuntimeOption("dalvik.vm.profile.interval-us", profileInterval, "-Xprofile-interval:");
// Coefficient for period backoff. The the period is multiplied
// by this value after each profile run.
parseRuntimeOption("dalvik.vm.profile.backoff-coeff", profileBackoff, "-Xprofile-backoff:");
// Top K% of samples that are considered relevant when
// deciding if the app should be recompiled.
parseRuntimeOption("dalvik.vm.profile.top-k-thr",
profileTopKThreshold,
"-Xprofile-top-k-threshold:");
// The threshold after which a change in the structure of the
// top K% profiled samples becomes significant and triggers
// recompilation. A change in profile is considered
// significant if X% (top-k-change-threshold) of the top K%
// (top-k-threshold property) samples has changed.
parseRuntimeOption("dalvik.vm.profile.top-k-ch-thr",
profileTopKChangeThreshold,
"-Xprofile-top-k-change-threshold:");
// Type of profile data.
parseRuntimeOption("dalvik.vm.profiler.type", profileType, "-Xprofile-type:");
// Depth of bounded stack data
parseRuntimeOption("dalvik.vm.profile.stack-depth",
profileMaxStackDepth,
"-Xprofile-max-stack-depth:");
/*
* Tracing options.
*/
property_get("dalvik.vm.method-trace", propBuf, "false");
if (strcmp(propBuf, "true") == 0) {
addOption("-Xmethod-trace");
parseRuntimeOption("dalvik.vm.method-trace-file",
methodTraceFileBuf,
"-Xmethod-trace-file:");
parseRuntimeOption("dalvik.vm.method-trace-file-siz",
methodTraceFileSizeBuf,
"-Xmethod-trace-file-size:");
property_get("dalvik.vm.method-trace-stream", propBuf, "false");
if (strcmp(propBuf, "true") == 0) {
addOption("-Xmethod-trace-stream");
}
}
// Native bridge library. "0" means that native bridge is disabled.
property_get("ro.dalvik.vm.native.bridge", propBuf, "");
if (propBuf[0] == '\0') {
ALOGW("ro.dalvik.vm.native.bridge is not expected to be empty");
} else if (strcmp(propBuf, "0") != 0) {
snprintf(nativeBridgeLibrary, sizeof("-XX:NativeBridge=") + PROPERTY_VALUE_MAX,
"-XX:NativeBridge=%s", propBuf);
addOption(nativeBridgeLibrary);
}
#if defined(__LP64__)
const char* cpu_abilist_property_name = "ro.product.cpu.abilist64";
#else
const char* cpu_abilist_property_name = "ro.product.cpu.abilist32";
#endif // defined(__LP64__)
property_get(cpu_abilist_property_name, propBuf, "");
if (propBuf[0] == '\0') {
ALOGE("%s is not expected to be empty", cpu_abilist_property_name);
return -1;
}
snprintf(cpuAbiListBuf, sizeof(cpuAbiListBuf), "--cpu-abilist=%s", propBuf);
addOption(cpuAbiListBuf);
// Dalvik-cache pruning counter.
parseRuntimeOption("dalvik.vm.zygote.max-boot-retry", cachePruneBuf,
"-Xzygote-max-boot-retry=");
/*
* When running with debug.generate-debug-info, add --generate-debug-info to
* the compiler options so that the boot image, if it is compiled on device,
* will include native debugging information.
*/
property_get("debug.generate-debug-info", propBuf, "");
if (strcmp(propBuf, "true") == 0) {
addOption("-Xcompiler-option");
addOption("--generate-debug-info");
addOption("-Ximage-compiler-option");
addOption("--generate-debug-info");
}
/*
* Retrieve the build fingerprint and provide it to the runtime. That way, ANR dumps will
* contain the fingerprint and can be parsed.
*/
parseRuntimeOption("ro.build.fingerprint", fingerprintBuf, "-Xfingerprint:");
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\n");
return -1;
}
return 0;
}
函数这么长，挑拣几个重要的描述：
dalvik.vm.checkjni:检测jni选项，会影响jni运行速度
dalvik.vm.execution-mode:虚拟机解释器模式：可移植、快速解释、即时编译Just-in-time
dalvik.vm.stack-trace-file:虚拟机traces文件路径，如果应用程序anr无响应会生成此文件，通常为/data/anr/traces.txt
dalvik.vm.heapstartsize:虚拟机堆内存启动大小
dalvik.vm.heapsize:虚拟机堆大小
dalvik.vm.heapgrowthlimit：堆大小增长限制大小
dalvik.vm.heapminfree/dalvik.vm.heapmaxfree:最小最大堆空闲大小
ro.dalvik.vm.native.bridge:native代码转换桥库，通常在模拟器会有值
其他的就不说明了(看不懂)
解析解析完这些参数开始启动虚拟机了
通过读取persist.sys.dalvik.vm.lib.2的内容判断启动的是dalvik虚拟机还是art虚拟机。
虚拟机启动完成之后开始反射ZygoteInitJava类的main函数
public static void main(String argv[]) {
try {
RuntimeInit.enableDdms();
// Start profiling the zygote initialization.
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;
} else if (argv[i].startsWith(ABI_LIST_ARG)) {
abiList = argv[i].substring(ABI_LIST_ARG.length());
} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
socketName = argv[i].substring(SOCKET_NAME_ARG.length());
} else {
throw new RuntimeException("Unknown command line argument: " + argv[i]);
}
}
if (abiList == null) {
throw new RuntimeException("No ABI list supplied.");
}
registerZygoteSocket(socketName);//创建ZygoteSocket
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
preload();//加载预加载的类，资源，共享库等
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
gcAndFinalize();//释放且回收一次内存
// Disable tracing so that forked processes do not inherit stale tracing tags from
// Zygote.
Trace.setTracingEnabled(false);
if (startSystemServer) { //是否启动系统服务
startSystemServer(abiList, socketName);
}
Log.i(TAG, "Accepting command socket connections");
runSelectLoop(abiList);//开始不断的轮询，等待ams到进程创建消息来fork子进程
closeServerSocket();
} catch (MethodAndArgsCaller caller) {
caller.run();
} catch (RuntimeException ex) {
Log.e(TAG, "Zygote died with exception", ex);
closeServerSocket();
throw ex;
}
}
通过之前传递的参数可得知需要启动SystemServer，
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=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1032,3001,3002,3003,3006,3007",
"--capabilities=" + capabilities + "," + capabilities,
"--nice-name=system_server",
"--runtime-args",
"com.android.server.SystemServer",
};
这是参数属性，足以让SystemServer掌控整个android系统(天命之子)。
关注到args最后一个参数，后续肯定会执行SystemServer来启动android所有服务。这时Zygote.forkSystemServer 将创建名为system_server的进程并将com.android.server.SystemServer传给system_server作为启动类。
接下来执行在system_server的函数handleSystemServerProcess将会被执行到，handleSystemServerProcess将会调用RuntimeInit.java的zygoteInit方法
public static final void zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
throws ZygoteInit.MethodAndArgsCaller {
if (DEBUG) Slog.d(TAG, "RuntimeInit: Starting application from zygote");
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "RuntimeInit");
redirectLogStreams(); //重定向System.out/err 内容到Log设备
commonInit();
nativeZygoteInit();
applicationInit(targetSdkVersion, argv, classLoader);
}
applicationInit(targetSdkVersion, argv, classLoader); //开始真正的调用SystemServer中的main函数，这是它的任务已经完成。
之前app_process除了能启动Zygote还可以启动其他应用程序
直接查看RuntimeInit的main函数
public static final void main(String[] argv) {
enableDdms();
if (argv.length == 2 && argv[1].equals("application")) {
if (DEBUG) Slog.d(TAG, "RuntimeInit: Starting application");
redirectLogStreams();
} else {
if (DEBUG) Slog.d(TAG, "RuntimeInit: Starting tool");
}
commonInit();
/*
* Now that we're running in interpreted code, call back into native code
* to run the system.
*/
nativeFinishInit();
if (DEBUG) Slog.d(TAG, "Leaving RuntimeInit!");
}
如果是应用，需要重定向System.err/out流到Log设备，commonInit()是时区和http代理到设置等。nativeFinishInit()最终将通过jni调用
/*
* Code written in the Java Programming Language calls here from main().
*/
static void com_android_internal_os_RuntimeInit_nativeFinishInit(JNIEnv* env, jobject clazz)
{
gCurRuntime->onStarted();
}
回到app_main.cpp到虚函数onStarted中。
virtual void onStarted()
{
sp proc = ProcessState::self();
ALOGV("App process: starting thread pool.\n");
proc->startThreadPool();
AndroidRuntime* ar = AndroidRuntime::getRuntime();
ar->callMain(mClassName, mClass, mArgs);
IPCThreadState::self()->stopProcess();
}
这里调用需要ProcessState来进程binder通讯，直到当前进main函数执行完毕之后才停止进程。常见到使用场景有am,pm 等文件
#!/system/bin/sh
#
# Script to start "am" on the device, which has a very rudimentary
# shell.
#
base=/system
export CLASSPATH=$base/framework/am.jar
exec app_process $base/bin com.android.commands.am.Am "$@"
ps >> /data/misc/logd/record.ps //加到调试日志，忽略。
至此整个Zygote分析完成。