请求 AMS 创建应用服务进程
Launcher 通过调用 AMS 请求创建应用程序的进程
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {
.....
// 获取要创建应用程序进程的用户 ID
final int userId = UserHandle.getUserId(app.uid);
int uid = app.uid;
// 给用户组的 id 进行赋值
int[] gids = null;
gids[0] = UserHandle.getSharedAppGid(UserHandle.getAppId(uid));
gids[1] = UserHandle.getCacheAppGid(UserHandle.getAppId(uid));
gids[2] = UserHandle.getUserGid(UserHandle.getUserId(uid));
// 启动进程
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith, entryPointArgs);
}
Process 的实例对象是 ZygoteProcess，这里是请求 ZygoteProcess 创建一个进程，并且创建成功后悔调用它的 main 函数
frameworks/base/core/java/android/os/ZygoteProcess.java
public final Process.ProcessStartResult start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int debugFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String abi,
String instructionSet,
String appDataDir,
String invokeWith,
String[] zygoteArgs) {
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
debugFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
}
start和startViaZygote实际上是通过 openZygoteSocketIfNeed 函数请求和 Zygote 服务建立 Socket 通信
private ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {
if (primaryZygoteState == null || primaryZygoteState.isClosed()) {
try {
primaryZygoteState = ZygoteState.connect(mSocket);
} catch (IOException ioe) {
throw new ZygoteStartFailedEx("Error connecting to primary zygote", ioe);
}
}
if (primaryZygoteState.matches(abi)) {
return primaryZygoteState;
}
// The primary zygote didn't match. Try the secondary.
if (secondaryZygoteState == null || secondaryZygoteState.isClosed()) {
try {
secondaryZygoteState = ZygoteState.connect(mSecondarySocket);
} catch (IOException ioe) {
throw new ZygoteStartFailedEx("Error connecting to secondary zygote", ioe);
}
}
}
ZygoteInit 服务接收到 AMS 的 Socket 链接
Zygote 服务在被 init 服务创建的时候就启动了一个 Socket 服务，等待着 AMS 的接入
zygoteServer.runSelectLoop(abiList)；
ZygoteServer 的 runSelectLoop
frameworks/base/core/java/com/android/internal/os/ZygoteServer.java
在请求第一次进入的时候，会将请求放入到集合中管理，再发起下一次轮训的时候会调用 ZygoteConnection 的 runOnce 方法解析请求
Runnable runSelectLoop(String abiList) {
ArrayList<FileDescriptor> socketFDs = new ArrayList<>();
ArrayList<ZygoteConnection> peers = new ArrayList<>();
while (true) {
....
for (int i = pollFds.length - 1; i >= 0; --i) {
if ((pollFds[i].revents & POLLIN) == 0) {
continue;
}
if (i == 0) {
ZygoteConnection newPeer = acceptCommandPeer(abiList);
peers.add(newPeer);
fds.add(newPeer.getFileDesciptor());
} else {
boolean done = peers.get(i).runOnce(this);
if (done) {
peers.remove(i);
fds.remove(i);
}
}
}
....
}
}
ZygoteConnection 的 runOnce 方法
- 解析启动进程的参数
- 创建应用的进程
- 处理子进程
boolean runOnce(ZygoteServer zygoteServer) throws Zygote.MethodAndArgsCaller {
Arguments parsedArgs = null;
FileDescriptor[] descriptors;
try {
args = readArgumentList();
// 根据传入的参数创建进程
pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,
parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,
parsedArgs.niceName, fdsToClose, fdsToIgnore, parsedArgs.instructionSet,
parsedArgs.appDataDir);
}catch(IOException ex){
return true;
}
// 创建好进程，让后续的代码运行在自进程中
// 如果在子进程中，关闭之前为 Zygote 创建的服务，因为子进程是 fork 自 zygote 的，会持有 zygote 的全部内容。
if (pid == 0) {
// in child
zygoteServer.closeServerSocket();
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
// 处理子进程
handleChildProc(parsedArgs, descriptors, childPipeFd, newStderr);
// should never get here, the child is expected to either
// throw Zygote.MethodAndArgsCaller or exec().
return true;
}
}
handleChildProc 会在fork出来的进程中运行,调用了 ZygoteInit
ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion,
parsedArgs.remainingArgs, null /* classLoader */);
调用 ZygoteInit 为当前的应用进程创建 Binder 线程池
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
public static final Runnable zygoteInit(int targetSdkVersion, long[] disabledCompatChanges,
String[] argv, ClassLoader classLoader) {
.....
RuntimeInit.commonInit();
// 创建 Binder 线程池
ZygoteInit.nativeZygoteInit();
// 调用应用程序的 ActivityThread 的 main 函数
return RuntimeInit.applicationInit(targetSdkVersion,disabledCompatChanges, argv,
classLoader);
}
RuntimeInit.application 会调用 ActivityThread 的 main 函数
protected static Runnable applicationInit(int targetSdkVersion, long[] disabledCompatChanges,
String[] argv, ClassLoader classLoader) {
// 在新的进程环境下调用 ActivityThread 的 main 函数
invokeStaticMain(args.startClass, args.startArgs, classLoader);
}
ActivityThread 的 main 函数
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
// End of event ActivityThreadMain.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
Looper.loop();
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