Android S从桌面点击图标启动APP流程 (六)

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>
                                                          pkgDataInfoMap,
                                                  @Nullable Map>
                                                          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>
                                                              pkgDataInfoMap,
                                                      @Nullable Map>
                                                              allowlistedDataInfoList,
                                                      boolean bindMountAppsData,
                                                      boolean bindMountAppStorageDirs,
                                                      @Nullable String[] extraArgs)
                                                      throws ZygoteStartFailedEx {
        ArrayList argsForZygote = new ArrayList<>();
 
        // --runtime-args, --setuid=, --setgid=,
        // and --setgroups= must go first
        argsForZygote.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 list
        if (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 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

太多了，写不下去了，本系列暂停更新。😂