Zygote进程

android12-release
Android系统启动
 init进程 – 干了啥事

system/core/init/init.cpp
system/core/rootdir/init.rc
frameworks/base/cmds/app_process/app_main.cpp
frameworks/base/core/jni/AndroidRuntime.cpp
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
frameworks/base/core/java/com/android/internal/os/Zygote.java

Zygote.rc文件

Zygote是由init进程通过解析init.zygote.rc文件而创建的，zygote所对应的可执行程序app_process，所对应的源文件是App_main.cpp，进程名为zygote。
在这里插入图片描述
init.zygote32.rc文件

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
    class main
    priority -20
    user root
    group root readproc reserved_disk
    socket zygote stream 660 root system
    socket usap_pool_primary stream 660 root system
    onrestart exec_background - system system -- /system/bin/vdc volume abort_fuse
    onrestart write /sys/power/state on
    onrestart restart audioserver
    onrestart restart cameraserver
    onrestart restart media
    onrestart restart netd
    onrestart restart wificond
    writepid /dev/cpuset/foreground/tasks
    critical window=${zygote.critical_window.minute:-off} target=zygote-fatal

init.zygote64.rc文件

service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
    class main
    priority -20
    user root
    group root readproc reserved_disk
    socket zygote stream 660 root system
    socket usap_pool_primary stream 660 root system
    onrestart exec_background - system system -- /system/bin/vdc volume abort_fuse
    onrestart write /sys/power/state on
    onrestart restart audioserver
    onrestart restart cameraserver
    onrestart restart media
    onrestart restart netd
    onrestart restart wificond
    writepid /dev/cpuset/foreground/tasks
    critical window=${zygote.critical_window.minute:-off} target=zygote-fatal

??创建叫"zygote"的service结构体；
??创建用于"socket"通信的socketinfo结构体；
??创建"onrestart"的action结构体。Zygote进程能够重启的地方。

??Zygote服务会随着main class的启动而启动，zygote所对应的可执行文件是/system/bin/app_processXX，通过调用pid =fork()创建子进程，通过execve(svc->args[0], (char**)svc->args, (char**) ENV)，进入App_main.cpp的main()函数。

init 解析 /system/etc/init/hw/init.${ro.zygote}.rc 文件启动Zygote进程
在这里插入图片描述

Zygote启动过程

app_main#main

frameworks/base/cmds/app_process/app_main.cpp

strcmp(arg, "--zygote") zygote为true，niceName = ZYGOTE_NICE_NAME区分32位、64位系统
strcmp(arg, "--start-system-server") startSystemServer为true
runtime.setArgv0(niceName.string(), true /* setProcName */);设置进程名
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);

#if defined(__LP64__)
static const char ABI_LIST_PROPERTY[] = "ro.product.cpu.abilist64";
static const char ZYGOTE_NICE_NAME[] = "zygote64";
#else
static const char ABI_LIST_PROPERTY[] = "ro.product.cpu.abilist32";
static const char ZYGOTE_NICE_NAME[] = "zygote";
#endif

int main(int argc, char* const argv[])
{
//。。。 。。。
    while (i < argc) {
        const char* arg = argv[i++];
        if (strcmp(arg, "--zygote") == 0) {
            zygote = true;
            niceName = ZYGOTE_NICE_NAME;
        } 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.setTo(arg + 12);
        } else if (strncmp(arg, "--", 2) != 0) {
            className.setTo(arg);
            break;
        } else {
            --i;
            break;
        }
    }
//。。。 。。。
        if (startSystemServer) {
            args.add(String8("start-system-server"));
        }
//。。。 。。。
    if (!niceName.isEmpty()) {
        runtime.setArgv0(niceName.string(), true /* setProcName */);
    }
 
    if (zygote) {
        runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
    } else if (className) {
        runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
    } else {
        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
        app_usage();
        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
    }
}

AndroidRuntime::start

frameworks/base/core/jni/include/android_runtime/AndroidRuntime.h
frameworks/base/core/jni/AndroidRuntime.cpp

primary_zygote = true
startVm()创建启动java虚拟机
startReg() register_jni_procs中JNI方法注册
env->CallStaticVoidMethod(startClass, startMeth, strArray) 这里startClass为"com.android.internal.os.ZygoteInit"，startMeth为main()方法
free(slashClassName) 释放相应对象的内存空间

void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
//。。。 。。。
    /*
     * '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) {
            primary_zygote = true;
           /* 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)));
        }
    }
//。。。 。。。
    /* start the virtual machine */
    JniInvocation jni_invocation;
    jni_invocation.Init(NULL);
    JNIEnv* env;
    if (startVm(&mJavaVM, &env, zygote, primary_zygote) != 0) {
        return;
    }
    onVmCreated(env);

    /*
     * Register android functions.
     */
    if (startReg(env) < 0) {
        ALOGE("Unable to register all android natives\n");
        return;
    }
//。。。 。。。
    /*
     * Start VM.  This thread becomes the main thread of the VM, and will
     * not return until the VM exits.
     */
    char* slashClassName = toSlashClassName(className != NULL ? 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 {
            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");
}

JNI到Java层

ZygoteInit.main

frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

RuntimeInit.preForkInit()中RuntimeInit.enableDdms()
startSystemServer = true
zygoteServer = new ZygoteServer(isPrimaryZygote) 为Zygote注册socket
forkSystemServer() 启动SystemServer
caller = zygoteServer.runSelectLoop(abiList); 进入循环模式，Zygote采用高效的I/O多路复用机制，保证在没有客户端连接请求或数据处理时休眠，否则响应客户端的请求。等待AMS请求。

    public static void main(String[] argv) {
        ZygoteServer zygoteServer = null;

        // Mark zygote start. This ensures that thread creation will throw
        // an error.
        ZygoteHooks.startZygoteNoThreadCreation();

        // Zygote goes into its own process group.
        try {
            Os.setpgid(0, 0);
        } catch (ErrnoException ex) {
            throw new RuntimeException("Failed to setpgid(0,0)", ex);
        }

        Runnable caller;
        try {
            // Store now for StatsLogging later.
            final long startTime = SystemClock.elapsedRealtime();
            final boolean isRuntimeRestarted = "1".equals(
                    SystemProperties.get("sys.boot_completed"));

            String bootTimeTag = Process.is64Bit() ? "Zygote64Timing" : "Zygote32Timing";
            TimingsTraceLog bootTimingsTraceLog = new TimingsTraceLog(bootTimeTag,
                    Trace.TRACE_TAG_DALVIK);
            bootTimingsTraceLog.traceBegin("ZygoteInit");
            RuntimeInit.preForkInit();

            boolean startSystemServer = false;
            String zygoteSocketName = "zygote";
            String abiList = null;
            boolean enableLazyPreload = false;
            for (int i = 1; i < argv.length; i++) {
                if ("start-system-server".equals(argv[i])) {
                    startSystemServer = true;
                } else if ("--enable-lazy-preload".equals(argv[i])) {
                    enableLazyPreload = 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)) {
                    zygoteSocketName = argv[i].substring(SOCKET_NAME_ARG.length());
                } else {
                    throw new RuntimeException("Unknown command line argument: " + argv[i]);
                }
            }

            final boolean isPrimaryZygote = zygoteSocketName.equals(Zygote.PRIMARY_SOCKET_NAME);
            if (!isRuntimeRestarted) {
                if (isPrimaryZygote) {
                    FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME_REPORTED,
                            BOOT_TIME_EVENT_ELAPSED_TIME__EVENT__ZYGOTE_INIT_START,
                            startTime);
                } else if (zygoteSocketName.equals(Zygote.SECONDARY_SOCKET_NAME)) {
                    FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME_REPORTED,
                            BOOT_TIME_EVENT_ELAPSED_TIME__EVENT__SECONDARY_ZYGOTE_INIT_START,
                            startTime);
                }
            }

            if (abiList == null) {
                throw new RuntimeException("No ABI list supplied.");
            }

            // In some configurations, we avoid preloading resources and classes eagerly.
            // In such cases, we will preload things prior to our first fork.
            if (!enableLazyPreload) {
                bootTimingsTraceLog.traceBegin("ZygotePreload");
                EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
                        SystemClock.uptimeMillis());
                preload(bootTimingsTraceLog);
                EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
                        SystemClock.uptimeMillis());
                bootTimingsTraceLog.traceEnd(); // ZygotePreload
            }

            // Do an initial gc to clean up after startup
            bootTimingsTraceLog.traceBegin("PostZygoteInitGC");
            gcAndFinalize();
            bootTimingsTraceLog.traceEnd(); // PostZygoteInitGC

            bootTimingsTraceLog.traceEnd(); // ZygoteInit

            Zygote.initNativeState(isPrimaryZygote);

            ZygoteHooks.stopZygoteNoThreadCreation();

            zygoteServer = new ZygoteServer(isPrimaryZygote);

            if (startSystemServer) {
                Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer);

                // {@code r == null} in the parent (zygote) process, and {@code r != null} in the
                // child (system_server) process.
                if (r != null) {
                    r.run();
                    return;
                }
            }

            Log.i(TAG, "Accepting command socket connections");

            // The select loop returns early in the child process after a fork and
            // loops forever in the zygote.
            caller = zygoteServer.runSelectLoop(abiList);
        } catch (Throwable ex) {
            Log.e(TAG, "System zygote died with fatal exception", ex);
            throw ex;
        } finally {
            if (zygoteServer != null) {
                zygoteServer.closeServerSocket();
            }
        }

        // We're in the child process and have exited the select loop. Proceed to execute the
        // command.
        if (caller != null) {
            caller.run();
        }
    }

forkSystemServer

pid = Zygote.forkSystemServer准备参数并fork新进程，从上面可以看出SystemServer进程参数信息为uid=1000,gid=1000,进程名为sytem_server，

    private static Runnable forkSystemServer(String abiList, String socketName,
            ZygoteServer zygoteServer) {
//。。。 。。。
        /* Hardcoded command line to start the system server */
        String[] args = {
                "--setuid=1000",
                "--setgid=1000",
                "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,"
                        + "1024,1032,1065,3001,3002,3003,3006,3007,3009,3010,3011",
                "--capabilities=" + capabilities + "," + capabilities,
                "--nice-name=system_server",
                "--runtime-args",
                "--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT,
                "com.android.server.SystemServer",
        };
        ZygoteArguments parsedArgs;
//。。。 。。。
            /* Request to fork the system server process */
            pid = Zygote.forkSystemServer(
                    parsedArgs.mUid, parsedArgs.mGid,
                    parsedArgs.mGids,
                    parsedArgs.mRuntimeFlags,
                    null,
                    parsedArgs.mPermittedCapabilities,
                    parsedArgs.mEffectiveCapabilities);
        } catch (IllegalArgumentException ex) {
            throw new RuntimeException(ex);
        }

        /* For child process */
        if (pid == 0) {
            if (hasSecondZygote(abiList)) {
                waitForSecondaryZygote(socketName);
            }

            zygoteServer.closeServerSocket();
            return handleSystemServerProcess(parsedArgs);
        }

        return null;
    }

frameworks/base/core/java/com/android/internal/os/Zygote.java

    static int forkSystemServer(int uid, int gid, int[] gids, int runtimeFlags,
            int[][] rlimits, long permittedCapabilities, long effectiveCapabilities) {
        ZygoteHooks.preFork();

        int pid = nativeForkSystemServer(
                uid, gid, gids, runtimeFlags, rlimits,
                permittedCapabilities, effectiveCapabilities);

        // Set the Java Language thread priority to the default value for new apps.
        Thread.currentThread().setPriority(Thread.NORM_PRIORITY);

        ZygoteHooks.postForkCommon();
        return pid;
    }