2025年System_Server与Zygote共存亡

科技前沿 • 2025-01-16 19:56 • 阅读 43

大家好，我是讯享网，很高兴认识大家。

Zygote孵化System_server的最后阶段ForkAndSpecializeCommon里会调用SetSigChldHandler设置信号处理函数。SetSigChldHandler定义了信号处理函数SigChldHandler，当信号SIGCHLD到来的时候，会进入信号处理函数。如果子进程SystemServer挂了，Zygote就会自杀。从而导致Zygote重启。

frameworks/base/core/jni/com_android_internal_os_Zygote.cpp static void SigChldHandler(int /*signal_number*/) { pid_t pid; int status; //Zygote监听所有子进程的存亡 while ((pid = waitpid(-1, &status, WNOHANG)) > 0) { //某一个子进程挂了 if (WIFSIGNALED(status)) { if (WTERMSIG(status) != SIGKILL) { ALOGI("Process %d exited due to signal (%d)", pid, WTERMSIG(status)); } } //如果挂掉的是SystemServer if (pid == gSystemServerPid) { ALOGE("Exit zygote because system server (%d) has terminated", pid); kill(getpid(), SIGKILL); //Zygote自杀 } } }

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而如果Zygote收到被kill的信号，会调用kill(-pid_, SIGKILL)，pid < 0将该信号发送给其进程组id等于pid的绝对值的进程组，导致System_Server被杀。系统重启。

讯享网

讯享网system/core/init/service.cpp bool ServiceManager::ReapOneProcess() { ...... if (WIFEXITED(status)) { NOTICE("%s exited with status %d\n", name.c_str(), WEXITSTATUS(status)); } else if (WIFSIGNALED(status)) { NOTICE("%s killed by signal %d\n", name.c_str(), WTERMSIG(status)); } else if (WIFSTOPPED(status)) { NOTICE("%s stopped by signal %d\n", name.c_str(), WSTOPSIG(status)); } else { NOTICE("%s state changed", name.c_str()); } if (svc->Reap()) { waiting_for_exec = false; RemoveService(*svc); } ...... } bool Service::Reap() { if (!(flags_ & SVC_ONESHOT) || (flags_ & SVC_RESTART)) { NOTICE("Service '%s' (pid %d) killing any children in process group\n", name_.c_str(), pid_); kill(-pid_, SIGKILL); //pid < 0将该信号发送给其进程组id等于pid的绝对值的进程组，但是不包含某些系统进程！ } ................. }

导致Zygote重启的一些事件，从init*rc可以看出，
Zygote：挂掉会触发media、netd以及子进程(包括System_Server进程)重启；
System_Server: 挂掉触发zygote重启;
surfaceflinger：重启触发zygote重启;
servicemanager: 重启触发zygote重启

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server class main socket zygote stream 660 root system onrestart write /sys/android_power/request_state wake onrestart write /sys/power/state on onrestart restart media onrestart restart netd service servicemanager /system/bin/servicemanager class core user system group system critical onrestart restart healthd onrestart restart zygote onrestart restart media onrestart restart surfaceflinger onrestart restart drm service surfaceflinger /system/bin/surfaceflinger class core user system group graphics drmrpc onrestart restart zygote

参考资料
http://gityuan.com/2016/02/05/android-init/
http://gityuan.com/2016/02/13/android-zygote/
http://gityuan.com/2016/02/14/android-system-server/
http://gityuan.com/2016/02/20/android-system-server-2/
http://www.jianshu.com/p/98cf2c9b5dee

2025年System_Server与Zygote共存亡

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