进程终止分析之一

1, 概述

在系统内存较低时就会杀死一些进程,最明显的在卸载一个apk之前会杀死该apk所在的进程。

在PMS的deletePackageLI方法中会调用killApplication方法杀死进程。

因此,本文以killApplication方法为例来论述杀死进程的过程。

2, 进程终止

流程图如下,

PMS的killApplication方法如下,

private void killApplication(String pkgName, int appId, String reason) {        // Request the ActivityManager to kill the process(only for existing packages)        // so that we do not end up in a confused state while the user is still using the older        // version of the application while the new one gets installed.        IActivityManager am = ActivityManagerNative.getDefault();        if (am != null) {            try {                am.killApplicationWithAppId(pkgName, appId, reason);            } catch (RemoteException e) {            }        }    }

直接调用AMS的killApplicationWithAppId方法,三个参数,分别是apk的包名,ID号以及杀死进程的原因。

@Override    public void killApplicationWithAppId(String pkg, int appid, String reason) {        if (pkg == null) {            return;        }        // Make sure the uid is valid.        if (appid < 0) {            Slog.w(TAG, "Invalid appid specified for pkg : " + pkg);            return;        }        int callerUid = Binder.getCallingUid();        // Only the system server can kill an application        if (UserHandle.getAppId(callerUid) == Process.SYSTEM_UID) {            // Post an aysnc message to kill the application            Message msg = mHandler.obtainMessage(KILL_APPLICATION_MSG);            msg.arg1 = appid;            msg.arg2 = 0;            Bundle bundle = new Bundle();            bundle.putString("pkg", pkg);            bundle.putString("reason", reason);            msg.obj = bundle;            mHandler.sendMessage(msg);        } else {            throw new SecurityException(callerUid + " cannot kill pkg: " +                    pkg);        }    }

发送KILL_APPLICATION_MSG消息,内部类MainHandler对该消息处理如下,

case KILL_APPLICATION_MSG: {                synchronized (ActivityManagerService.this) {                    int appid = msg.arg1;                    boolean restart = (msg.arg2 == 1);                    Bundle bundle = (Bundle)msg.obj;                    String pkg = bundle.getString("pkg");                    String reason = bundle.getString("reason");                    forceStopPackageLocked(pkg, appid, restart, false, true, false,                            false, UserHandle.USER_ALL, reason);                }            } break;

调用forceStopPackageLocked的方法,发送消息实质就是切换一下线程,到主线程中终止进程。killPackageProcessesLocked逻辑简单。

主要功能如下:

1,调用killPackageProcessesLocked方法杀死进程。

boolean didSomething = killPackageProcessesLocked(packageName, appId, userId,                -100, callerWillRestart, true, doit, evenPersistent,                packageName == null ? ("stop user " + userId) : ("stop " + packageName));

2,清理四大组件

  调用ActivityStackSupervisor的finishDisabledPackageActivitiesLocked方法清理apk所涉及的Activity

if (mStackSupervisor.finishDisabledPackageActivitiesLocked(                packageName, null, doit, evenPersistent, userId)) {            if (!doit) {                return true;            }            didSomething = true;        }

调用ActiveServices的bringDownDisabledPackageServicesLocked方法清理apk所涉及的Services

     if (mServices.bringDownDisabledPackageServicesLocked(                packageName, null, userId, evenPersistent, true, doit)) {            if (!doit) {                return true;            }            didSomething = true;        }

调用ProviderMap的collectPackageProvidersLocked方法搜集apk所涉及的Provider,

然后调用removeDyingProviderLocked方法清除

 if (packageName == null) {            // Remove all sticky broadcasts from this user.            mStickyBroadcasts.remove(userId);        }  ArrayList<ContentProviderRecord> providers = new ArrayList<>();  if (mProviderMap.collectPackageProvidersLocked(packageName, null, doit, evenPersistent,                userId, providers)) {            if (!doit) {                return true;            }            didSomething = true;        }        for (i = providers.size() - 1; i >= 0; i--) {            removeDyingProviderLocked(null, providers.get(i), true);        }

调用removeUriPermissionsForPackageLocked方法清理权限

   removeUriPermissionsForPackageLocked(packageName, userId, false);

调用BroadcastQueue的cleanupDisabledPackageReceiversLocked方法清理apk所涉及的Broadcast

 if (doit) {            for (i = mBroadcastQueues.length - 1; i >= 0; i--) {                didSomething |= mBroadcastQueues[i].cleanupDisabledPackageReceiversLocked(                        packageName, null, userId, doit);            }        }

forceStopPackageLocked方法中清理四大组件调用的方法如下,

Activity

ActivityStackSupervisor

finishDisabledPackageActivitiesLocked

Services

ActiveServices

bringDownDisabledPackageServicesLocked

Provider

ProviderMap

collectPackageProvidersLocked

Broadcast

BroadcastQueue

cleanupDisabledPackageReceiversLocked

首先看killPackageProcessesLocked方法

private final boolean killPackageProcessesLocked(String packageName, int appId,            int userId, int minOomAdj, boolean callerWillRestart, boolean allowRestart,            boolean doit, boolean evenPersistent, String reason) {        ArrayList<ProcessRecord> procs = new ArrayList<>();        // Remove all processes this package may have touched: all with the        // same UID (except for the system or root user), and all whose name        // matches the package name.        final int NP = mProcessNames.getMap().size();        for (int ip=0; ip<NP; ip++) {            SparseArray<ProcessRecord> apps = mProcessNames.getMap().valueAt(ip);            final int NA = apps.size();            for (int ia=0; ia<NA; ia++) {                ProcessRecord app = apps.valueAt(ia);                if (app.persistent && !evenPersistent) {                    // we don't kill persistent processes                    continue;                }                if (app.removed) {                    if (doit) {                        procs.add(app);                    }                    continue;                }                // Skip process if it doesn't meet our oom adj requirement.                if (app.setAdj < minOomAdj) {                    continue;                }                // If no package is specified, we call all processes under the                // give user id.                if (packageName == null) {                    if (userId != UserHandle.USER_ALL && app.userId != userId) {                        continue;                    }                    if (appId >= 0 && UserHandle.getAppId(app.uid) != appId) {                        continue;                    }                // Package has been specified, we want to hit all processes                // that match it.  We need to qualify this by the processes                // that are running under the specified app and user ID.                } else {                    final boolean isDep = app.pkgDeps != null                            && app.pkgDeps.contains(packageName);                    if (!isDep && UserHandle.getAppId(app.uid) != appId) {                        continue;                    }                    if (userId != UserHandle.USER_ALL && app.userId != userId) {                        continue;                    }                    if (!app.pkgList.containsKey(packageName) && !isDep) {                        continue;                    }                }                // Process has passed all conditions, kill it!                if (!doit) {                    return true;                }                app.removed = true;                procs.add(app);            }        }        int N = procs.size();        for (int i=0; i<N; i++) {            removeProcessLocked(procs.get(i), callerWillRestart, allowRestart, reason);        }        updateOomAdjLocked();        return N > 0;    }

该方法会遍历当前所有运行中的进程mProcessNames，筛选出被杀的目标进程：(也就是说满足以下任一条件都可以免死)

1.persistent进程：

2.进程setAdj < minOomAdj(默认为-100)：

3.非UserHandle.USER_ALL同时, 且进程的userId不相等：多用户模型下，不同用户下不能相互杀；

4.进程没有依赖该packageName, 且进程的AppId不相等;

5.进程没有依赖该packageName, 且该packageName没有运行在该进程.

 

通俗地来说就是：

•forceStop不杀系统persistent进程；

•当指定用户userId时，不杀其他用户空间的进程；

 

除此之外，以下情况则必然会成为被杀进程：

•进程已标记remove=true的进程，则会被杀；

•进程的pkgDeps中包含该packageName，则会被杀；

•进程的pkgList中包含该packageName，且该进程与包名所指定的AppId相等则会被杀；

 

进程的pkgList是在启动组件或者创建进程的过程向该队列添加的，代表的是该应用下有组件运行在该进程。

筛选出即将杀死的进程之后,首先调用removeProcessLocked杀死进程,然后调用updateOomAdjLocked方法更新其他进程的优先级。

removeProcessLocked方法如下,

private final boolean removeProcessLocked(ProcessRecord app,            boolean callerWillRestart, boolean allowRestart, String reason) {        final String name = app.processName;        final int uid = app.uid;        if (DEBUG_PROCESSES) Slog.d(TAG_PROCESSES,            "Force removing proc " + app.toShortString() + " (" + name + "/" + uid + ")");        removeProcessNameLocked(name, uid);        if (mHeavyWeightProcess == app) {            mHandler.sendMessage(mHandler.obtainMessage(CANCEL_HEAVY_NOTIFICATION_MSG,                    mHeavyWeightProcess.userId, 0));            mHeavyWeightProcess = null;        }        boolean needRestart = false;        if (app.pid > 0 && app.pid != MY_PID) {            int pid = app.pid;            synchronized (mPidsSelfLocked) {                mPidsSelfLocked.remove(pid);                mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);            }            mBatteryStatsService.noteProcessFinish(app.processName, app.info.uid);            if (app.isolated) {                mBatteryStatsService.removeIsolatedUid(app.uid, app.info.uid);            }            boolean willRestart = false;            if (app.persistent && !app.isolated) {                if (!callerWillRestart) {                    willRestart = true;                } else {                    needRestart = true;                }            }            app.kill(reason, true); //杀掉该进程            handleAppDiedLocked(app, willRestart, allowRestart); //清理该进程相关的信息            if (willRestart) {                removeLruProcessLocked(app); //对于persistent进程,则需要重新启动该进程                addAppLocked(app.info, false, null /* ABI override */);            }        } else {            mRemovedProcesses.add(app);        }        return needRestart;    }

调用app.kill()来杀进程会同时调用Process.kill和Process.killProcessGroup。

调用handleAppDiedLocked()来清理进程相关的信息。