Android9.0 Launcher启动Activity详解(二)

一.Process向Zygote发送创建进程请求

framework/base/core/java/android/os/Process.java
 public static ProcessStartResult start(@NonNull final String processClass,
                                           @Nullable 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>>
                                                   whitelistedDataInfoMap,
                                           boolean bindMountAppsData,
                                           boolean bindMountAppStorageDirs,
                                           @Nullable String[] zygoteArgs) {
        return ZYGOTE_PROCESS.start(processClass, niceName, uid, gid, gids,
                    runtimeFlags, mountExternal, targetSdkVersion, seInfo,
                    abi, instructionSet, appDataDir, invokeWith, packageName,
                    zygotePolicyFlags, isTopApp, disabledCompatChanges,
                    pkgDataInfoMap, whitelistedDataInfoMap, bindMountAppsData,
                    bindMountAppStorageDirs, zygoteArgs);
    }
framework/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>>
                                                          whitelistedDataInfoMap,
                                                  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, whitelistedDataInfoMap, 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);
        }
    }

从中看到最重要到实现是startViaZygote,看其实现

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>>
                                                              whitelistedDataInfoMap,
                                                      boolean bindMountAppsData,
                                                      boolean bindMountAppStorageDirs,
                                                      @Nullable String[] extraArgs)
            throws ZygoteStartFailedEx {
        ArrayList<String> argsForZygote = new ArrayList<>();

        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_READ) {
            argsForZygote.add("--mount-external-read");
        } else if (mountExternal == Zygote.MOUNT_EXTERNAL_WRITE) {
            argsForZygote.add("--mount-external-write");
        } else if (mountExternal == Zygote.MOUNT_EXTERNAL_FULL) {
            argsForZygote.add("--mount-external-full");
        } else if (mountExternal == Zygote.MOUNT_EXTERNAL_INSTALLER) {
            argsForZygote.add("--mount-external-installer");
        } else if (mountExternal == Zygote.MOUNT_EXTERNAL_LEGACY) {
            argsForZygote.add("--mount-external-legacy");
        } 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);

        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.
            return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi),
                    zygotePolicyFlags,
                    argsForZygote);
        }
    }

这里调用zygoteSendArgsAndGetResult方法,其argsForZygote为进程的启动参数,openZygoteSocketIfNeeded为Zygote和Socket流建立连接,我们看下其实现

 private ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {
        try {
            attemptConnectionToPrimaryZygote();

            if (primaryZygoteState.matches(abi)) {
                return primaryZygoteState;
            }

            if (mZygoteSecondarySocketAddress != null) {
                // The primary zygote didn't match. Try the secondary.
                attemptConnectionToSecondaryZygote();

                if (secondaryZygoteState.matches(abi)) {
                    return secondaryZygoteState;
                }
            }
        } catch (IOException ioe) {
            throw new ZygoteStartFailedEx("Error connecting to zygote", ioe);
        }

        throw new ZygoteStartFailedEx("Unsupported zygote ABI: " + abi);
    }

 attemptConnectionToPrimaryZygote会去建立连接,看其实现

  private void attemptConnectionToSecondaryZygote() throws IOException {
        if (secondaryZygoteState == null || secondaryZygoteState.isClosed()) {
            secondaryZygoteState =
                    ZygoteState.connect(mZygoteSecondarySocketAddress,
                            mUsapPoolSecondarySocketAddress);

            maybeSetApiDenylistExemptions(secondaryZygoteState, false);
            maybeSetHiddenApiAccessLogSampleRate(secondaryZygoteState);
        }
    }
static ZygoteState connect(@NonNull LocalSocketAddress zygoteSocketAddress,
                @Nullable LocalSocketAddress usapSocketAddress)
                throws IOException {

            DataInputStream zygoteInputStream;
            BufferedWriter zygoteOutputWriter;
            final LocalSocket zygoteSessionSocket = new LocalSocket();

            if (zygoteSocketAddress == null) {
                throw new IllegalArgumentException("zygoteSocketAddress can't be null");
            }

            try {
                zygoteSessionSocket.connect(zygoteSocketAddress);
                zygoteInputStream = new DataInputStream(zygoteSessionSocket.getInputStream());
                zygoteOutputWriter =
                        new BufferedWriter(
                                new OutputStreamWriter(zygoteSessionSocket.getOutputStream()),
                                Zygote.SOCKET_BUFFER_SIZE);
            } catch (IOException ex) {
                try {
                    zygoteSessionSocket.close();
                } catch (IOException ignore) { }

                throw ex;
            }

            return new ZygoteState(zygoteSocketAddress, usapSocketAddress,
                                   zygoteSessionSocket, zygoteInputStream, zygoteOutputWriter,
                                   getAbiList(zygoteOutputWriter, zygoteInputStream));
        }

        LocalSocket getUsapSessionSocket() throws IOException {
            final LocalSocket usapSessionSocket = new LocalSocket();
            usapSessionSocket.connect(this.mUsapSocketAddress);

            return usapSessionSocket;
        }

        boolean matches(String abi) {
            return mAbiList.contains(abi);
        }

        public void close() {
            try {
                mZygoteSessionSocket.close();
            } catch (IOException ex) {
                Log.e(LOG_TAG,"I/O exception on routine close", ex);
            }

            mClosed = true;
        }

        boolean isClosed() {
            return mClosed;
        }
    }

  LocalSocket zygoteSessionSocket = new LocalSocket()生成Socket流,然后zygoteSessionSocket.connect(zygoteSocketAddress),看下connect方法

framework/base/core/java/android/net/LocalSocket.java
public void connect(LocalSocketAddress endpoint) throws IOException {
        synchronized (this) {
            if (isConnected) {
                throw new IOException("already connected");
            }

            implCreateIfNeeded();
            impl.connect(endpoint, 0);
            isConnected = true;
            isBound = true;
        }
    }

实现为LocalSocketImpl类,看其实现

protected void connect(LocalSocketAddress address, int timeout)
                        throws IOException
    {        
        if (fd == null) {
            throw new IOException("socket not created");
        }

        connectLocal(fd, address.getName(), address.getNamespace().getId());
    }
    private native void connectLocal(FileDescriptor fd, String name,
            int namespace) throws IOException;

最后调用了底层connectLocal去实现连接,这里就不再进一步分析了。Socket和Zygote建立连接后,我们继续看下zygoteSendArgsAndGetResult的实现

 private Process.ProcessStartResult zygoteSendArgsAndGetResult(
            ZygoteState zygoteState, int zygotePolicyFlags, @NonNull ArrayList<String> args)
            throws ZygoteStartFailedEx {
        ...
        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);
    }
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();
            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);
        }
    }

这里主要就是把我们要启动的进程参数写入到了ZygoteState,这样就完成了向Zygote发生创建进程的任务请求。

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