Zygote.java源码分析

源码位置：frameworks/base/core/java/com/android/internal/os/Zygote.java

forkSystemServer方法

https://www.jianshu.com/p/bb96360b4084

335     public static int forkSystemServer(int uid, int gid, int[] gids, int runtimeFlags,
336             int[][] rlimits, long permittedCapabilities, long effectiveCapabilities) {
337         ZygoteHooks.preFork();
338         // Resets nice priority for zygote process.
339         resetNicePriority();
340         int pid = nativeForkSystemServer(
341                 uid, gid, gids, runtimeFlags, rlimits,
342                 permittedCapabilities, effectiveCapabilities);
343         // Enable tracing as soon as we enter the system_server.
344         if (pid == 0) {
345             Trace.setTracingEnabled(true, runtimeFlags);
346         }
347         ZygoteHooks.postForkCommon();
348         return pid;
349     }

→nativeForkSystemServer

nativeForkSystemServer方法实现位于frameworks/base/core/jni/com_android_internal_os_Zygote.cpp +1404,最终是调用了c语言的fork函数。

1404 static jint com_android_internal_os_Zygote_nativeForkSystemServer(
1405         JNIEnv* env, jclass, uid_t uid, gid_t gid, jintArray gids,
1406         jint runtime_flags, jobjectArray rlimits, jlong permitted_capabilities,
1407         jlong effective_capabilities) {
...
1417 
1418   pid_t pid = ForkCommon(env, true,
1419                          fds_to_close,
1420                          fds_to_ignore);
1421   if (pid == 0) {
1422       SpecializeCommon(env, uid, gid, gids, runtime_flags, rlimits,
1423                        permitted_capabilities, effective_capabilities,
1424                        MOUNT_EXTERNAL_DEFAULT, nullptr, nullptr, true,
1425                        false, nullptr, nullptr);
1426   } else if (pid > 0) {
1427       // The zygote process checks whether the child process has died or not.
1428       ALOGI("System server process %d has been created", pid);
1429       gSystemServerPid = pid;
1430       // There is a slight window that the system server process has crashed
1431       // but it went unnoticed because we haven't published its pid yet. So
1432       // we recheck here just to make sure that all is well.
1433       int status;
1434       if (waitpid(pid, &status, WNOHANG) == pid) {
1435           ALOGE("System server process %d has died. Restarting Zygote!", pid);
1436           RuntimeAbort(env, __LINE__, "System server process has died. Restarting Zygote!");
1437       }
1447   }
1448   return pid;
1449 }

上面利用waitpid监听SystemServer子进程，SystemServer挂了就会重启zygote进程。

 313 static void RuntimeAbort(JNIEnv* env, int line, const char* msg) {
 314   std::ostringstream oss;
 315   oss << __FILE__ << ":" << line << ": " << msg;
 316   env->FatalError(oss.str().c_str());
 317 }