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系列文章

Android S从桌面点击图标启动APP流程 (一)
Android S从桌面点击图标启动APP流程 (二)

Android S从桌面点击图标启动APP流程 (三)

Android S从桌面点击图标启动APP流程 (四)

Android S从桌面点击图标启动APP流程 (五)

Android 12的源码链接：

android 12 aosphttp://aospxref.com/android-12.0.0_r3/上文讲到了 Process.start, 这里接着往下讲解

ZygoteProcess#start

frameworks/base/core/java/android/os/ZygoteProcess.java

    public final Process.ProcessStartResult start(@NonNull final String processClass,final String niceName,int uid, int gid, @Nullable int[] gids,int runtimeFlags, int mountExternal,int targetSdkVersion,@Nullable String seInfo,@NonNull String abi,@Nullable String instructionSet,@Nullable String appDataDir,@Nullable String invokeWith,@Nullable String packageName,int zygotePolicyFlags,boolean isTopApp,@Nullable long[] disabledCompatChanges,@Nullable Map<String, Pair<String, Long>>pkgDataInfoMap,@Nullable Map<String, Pair<String, Long>>allowlistedDataInfoList,boolean bindMountAppsData,boolean bindMountAppStorageDirs,@Nullable String[] zygoteArgs) {// TODO (chriswailes): Is there a better place to check this value?if (fetchUsapPoolEnabledPropWithMinInterval()) {informZygotesOfUsapPoolStatus();}try {return startViaZygote(processClass, niceName, uid, gid, gids,runtimeFlags, mountExternal, targetSdkVersion, seInfo,abi, instructionSet, appDataDir, invokeWith, /*startChildZygote=*/ false,packageName, zygotePolicyFlags, isTopApp, disabledCompatChanges,pkgDataInfoMap, allowlistedDataInfoList, bindMountAppsData,bindMountAppStorageDirs, zygoteArgs);} catch (ZygoteStartFailedEx ex) {Log.e(LOG_TAG,"Starting VM process through Zygote failed");throw new RuntimeException("Starting VM process through Zygote failed", ex);}}

ZygoteProcess#startViaZygote

该过程主要工作是生成argsForZygote数组

frameworks/base/core/java/android/os/ZygoteProcess.java

    private Process.ProcessStartResult startViaZygote(@NonNull final String processClass,@Nullable final String niceName,final int uid, final int gid,@Nullable final int[] gids,int runtimeFlags, int mountExternal,int targetSdkVersion,@Nullable String seInfo,@NonNull String abi,@Nullable String instructionSet,@Nullable String appDataDir,@Nullable String invokeWith,boolean startChildZygote,@Nullable String packageName,int zygotePolicyFlags,boolean isTopApp,@Nullable long[] disabledCompatChanges,@Nullable Map<String, Pair<String, Long>>pkgDataInfoMap,@Nullable Map<String, Pair<String, Long>>allowlistedDataInfoList,boolean bindMountAppsData,boolean bindMountAppStorageDirs,@Nullable String[] extraArgs)throws ZygoteStartFailedEx {ArrayList<String> argsForZygote = new ArrayList<>();// --runtime-args, --setuid=, --setgid=,// and --setgroups= must go firstargsForZygote.add("--runtime-args");argsForZygote.add("--setuid=" + uid);argsForZygote.add("--setgid=" + gid);argsForZygote.add("--runtime-flags=" + runtimeFlags);if (mountExternal == Zygote.MOUNT_EXTERNAL_DEFAULT) {argsForZygote.add("--mount-external-default");} else if (mountExternal == Zygote.MOUNT_EXTERNAL_INSTALLER) {argsForZygote.add("--mount-external-installer");} else if (mountExternal == Zygote.MOUNT_EXTERNAL_PASS_THROUGH) {argsForZygote.add("--mount-external-pass-through");} else if (mountExternal == Zygote.MOUNT_EXTERNAL_ANDROID_WRITABLE) {argsForZygote.add("--mount-external-android-writable");}argsForZygote.add("--target-sdk-version=" + targetSdkVersion);// --setgroups is a comma-separated listif (gids != null && gids.length > 0) {final StringBuilder sb = new StringBuilder();sb.append("--setgroups=");final int sz = gids.length;for (int i = 0; i < sz; i++) {if (i != 0) {sb.append(',');}sb.append(gids[i]);}argsForZygote.add(sb.toString());}if (niceName != null) {argsForZygote.add("--nice-name=" + niceName);}if (seInfo != null) {argsForZygote.add("--seinfo=" + seInfo);}if (instructionSet != null) {argsForZygote.add("--instruction-set=" + instructionSet);}if (appDataDir != null) {argsForZygote.add("--app-data-dir=" + appDataDir);}if (invokeWith != null) {argsForZygote.add("--invoke-with");argsForZygote.add(invokeWith);}if (startChildZygote) {argsForZygote.add("--start-child-zygote");}if (packageName != null) {argsForZygote.add("--package-name=" + packageName);}if (isTopApp) {argsForZygote.add(Zygote.START_AS_TOP_APP_ARG);}
......argsForZygote.add(processClass);if (extraArgs != null) {Collections.addAll(argsForZygote, extraArgs);}synchronized(mLock) {// The USAP pool can not be used if the application will not use the systems graphics// driver.  If that driver is requested use the Zygote application start path.
根据当前的abi来选择与zygote还是zygote64来进行通信。return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi),zygotePolicyFlags,argsForZygote);}}

ZygoteProcess#zygoteSendArgsAndGetResult

这个方法的主要功能是通过socket通道向Zygote进程发送一个参数列表，然后进入阻塞等待状态，直到远端的socket服务端发送回来新创建的进程pid才返回。

frameworks/base/core/java/android/os/ZygoteProcess.java

    private Process.ProcessStartResult zygoteSendArgsAndGetResult(ZygoteState zygoteState, int zygotePolicyFlags, @NonNull ArrayList<String> args)throws ZygoteStartFailedEx {// Throw early if any of the arguments are malformed. This means we can// avoid writing a partial response to the zygote.for (String arg : args) {// Making two indexOf calls here is faster than running a manually fused loop due// to the fact that indexOf is an optimized intrinsic.if (arg.indexOf('\n') >= 0) {throw new ZygoteStartFailedEx("Embedded newlines not allowed");} else if (arg.indexOf('\r') >= 0) {throw new ZygoteStartFailedEx("Embedded carriage returns not allowed");}}/** See com.android.internal.os.ZygoteArguments.parseArgs()* Presently the wire format to the zygote process is:* a) a count of arguments (argc, in essence)* b) a number of newline-separated argument strings equal to count** After the zygote process reads these it will write the pid of* the child or -1 on failure, followed by boolean to* indicate whether a wrapper process was used.*/String msgStr = args.size() + "\n" + String.join("\n", args) + "\n";if (shouldAttemptUsapLaunch(zygotePolicyFlags, args)) {try {return attemptUsapSendArgsAndGetResult(zygoteState, msgStr);} catch (IOException ex) {// If there was an IOException using the USAP pool we will log the error and// attempt to start the process through the Zygote.Log.e(LOG_TAG, "IO Exception while communicating with USAP pool - "+ ex.getMessage());}}return attemptZygoteSendArgsAndGetResult(zygoteState, msgStr);}

ZygoteProcess#attemptZygoteSendArgsAndGetResult

frameworks/base/core/java/android/os/ZygoteProcess.java

    private Process.ProcessStartResult attemptZygoteSendArgsAndGetResult(ZygoteState zygoteState, String msgStr) throws ZygoteStartFailedEx {try {final BufferedWriter zygoteWriter = zygoteState.mZygoteOutputWriter;final DataInputStream zygoteInputStream = zygoteState.mZygoteInputStream;zygoteWriter.write(msgStr);zygoteWriter.flush();// Always read the entire result from the input stream to avoid leaving// bytes in the stream for future process starts to accidentally stumble// upon.Process.ProcessStartResult result = new Process.ProcessStartResult();
等待socket服务端-zygote返回新创建的进程pid;result.pid = zygoteInputStream.readInt();result.usingWrapper = zygoteInputStream.readBoolean();if (result.pid < 0) {throw new ZygoteStartFailedEx("fork() failed");}return result;} catch (IOException ex) {zygoteState.close();Log.e(LOG_TAG, "IO Exception while communicating with Zygote - "+ ex.toString());throw new ZygoteStartFailedEx(ex);}}

system_server进程通过调用attemptZygoteSendArgsAndGetResult()方法通过socket方式向Zygote进程发送消息，这样会唤醒Zygote进程，来响应socket客户端的请求（即system_server端），接下来的操作便是在Zygote来创建进程

ZygoteInit#main

然后会走进zygote进程创建进程，由于步骤太多，此处省略，直接到ActivityThread.main这里开始讲解。后文接着讲ActivityThread#main