思路
PakcageMS启动时添加Flag SCAN_NO_DEX, 当扫描执行目录时，跳过做Dex优化步骤，其次在SystemServer::startOtherServices时启动JobSchedule任务,延迟一分钟进行Dex任务；
1.1 扫描指定目录添加flag
public PackageManagerService(Context context, Installer installer, boolean factoryTest, boolean onlyCore) {
...
scanDirLI(customFrameworkDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR,
scanFlags | SCAN_NO_DEX, 0); //添加flag
...
}
1.2 SCAN_NO_DEX
private PackageParser.Package scanPackageDirtyLI(PackageParser.Package pkg, int parseFlags,
int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
...
if ((scanFlags & SCAN_NO_DEX) == 0) { // PackageMS启动时不做Dex优化
int result = mPackageDexOptimizer.performDexOpt(pkg, null /* instruction sets */,
forceDex, (scanFlags & SCAN_DEFER_DEX) != 0, false /* inclDependencies */);
if (result == PackageDexOptimizer.DEX_OPT_FAILED) {
throw new PackageManagerException(INSTALL_FAILED_DEXOPT, "scanPackageLI");
}
}
...
}
1.3 启动JobSchedule延迟Dex优化
private void startOtherServices() {
...
mSystemServiceManager.startService(JobSchedulerService.class);
traceBeginAndSlog("StartBackgroundDexOptService");
try {
BackgroundDexOptService.schedule(context);
} catch (Throwable e) {
reportWtf("starting BackgroundDexOptService", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
...
mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY);
...
}
1.4 BackgroundDexOptService延迟执行Dex优化
public class BackgroundDexOptService extends JobService {
static final String TAG = "BackgroundDexOptService";
static final long RETRY_LATENCY = 4 * AlarmManager.INTERVAL_HOUR;
static final int JOB_IDLE_OPTIMIZE = 800;
static final int JOB_POST_BOOT_UPDATE = 801;
private static ComponentName sDexoptServiceName = new ComponentName(
"android",
BackgroundDexOptService.class.getName());
/**
* Set of failed packages remembered across job runs.
*/
static final ArraySet sFailedPackageNames = new ArraySet();
/**
* Atomics set to true if the JobScheduler requests an abort.
*/
final AtomicBoolean mAbortPostBootUpdate = new AtomicBoolean(false);
final AtomicBoolean mAbortIdleOptimization = new AtomicBoolean(false);
/**
* Atomic set to true if one job should exit early because another job was started.
*/
final AtomicBoolean mExitPostBootUpdate = new AtomicBoolean(false);
private final File dataDir = Environment.getDataDirectory();
public static void schedule(Context context) {
JobScheduler js = (JobScheduler) context.getSystemService(Context.JOB_SCHEDULER_SERVICE);
// Schedule a one-off job which scans installed packages and updates
// out-of-date oat files.
js.schedule(new JobInfo.Builder(JOB_POST_BOOT_UPDATE, sDexoptServiceName)
.setMinimumLatency(TimeUnit.MINUTES.toMillis(1)) // 延迟一分钟
.setOverrideDeadline(TimeUnit.MINUTES.toMillis(1))
.build());
// Schedule a daily job which scans installed packages and compiles
// those with fresh profiling data.
js.schedule(new JobInfo.Builder(JOB_IDLE_OPTIMIZE, sDexoptServiceName)
.setRequiresDeviceIdle(true)
.setRequiresCharging(true)
.setPeriodic(TimeUnit.DAYS.toMillis(1)) // 每天
.build());
}
// Returns the current battery level as a 0-100 integer.
private int getBatteryLevel() {
IntentFilter filter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
Intent intent = registerReceiver(null, filter);
int level = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, -1);
int scale = intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
if (level < 0 || scale <= 0) {
// Battery data unavailable. This should never happen, so assume the worst.
return 0;
}
return (100 * level / scale);
}
private long getLowStorageThreshold() {
@SuppressWarnings("deprecation")
final long lowThreshold = StorageManager.from(this).getStorageLowBytes(dataDir);
if (lowThreshold == 0) {
Log.e(TAG, "Invalid low storage threshold");
}
return lowThreshold;
}
private boolean runPostBootUpdate(final JobParameters jobParams,
final PackageManagerService pm, final ArraySet pkgs) {
if (mExitPostBootUpdate.get()) {
// This job has already been superseded. Do not start it.
return false;
}
// Load low battery threshold from the system config. This is a 0-100 integer.
final int lowBatteryThreshold = getResources().getInteger(
com.android.internal.R.integer.config_lowBatteryWarningLevel);
final long lowThreshold = getLowStorageThreshold();
mAbortPostBootUpdate.set(false);
new Thread("BackgroundDexOptService_PostBootUpdate") {
@Override
public void run() {
for (String pkg : pkgs) {
if (mAbortPostBootUpdate.get()) {
// JobScheduler requested an early abort.
return;
}
if (mExitPostBootUpdate.get()) {
// Different job, which supersedes this one, is running.
break;
}
if (getBatteryLevel() < lowBatteryThreshold) {
// Rather bail than completely drain the battery.
break;
}
long usableSpace = dataDir.getUsableSpace();
if (usableSpace < lowThreshold) {
// Rather bail than completely fill up the disk.
Log.w(TAG, "Aborting background dex opt job due to low storage: " +
usableSpace);
break;
}
// Update package if needed. Note that there can be no race between concurrent
// jobs because PackageDexOptimizer.performDexOpt is synchronized.
// checkProfiles is false to avoid merging profiles during boot which
// might interfere with background compilation (b/28612421).
// Unfortunately this will also means that "pm.dexopt.boot=speed-profile" will
// behave differently than "pm.dexopt.bg-dexopt=speed-profile" but that's a
// trade-off worth doing to save boot time work.
pm.performDexOpt(pkg,
/* checkProfiles */ false,
PackageManagerService.REASON_BOOT,
/* force */ false);//dex优化
}
// Ran to completion, so we abandon our timeslice and do not reschedule.
jobFinished(jobParams, /* reschedule */ false);
}
}.start();
return true;
}
private boolean runIdleOptimization(final JobParameters jobParams,
final PackageManagerService pm, final ArraySet pkgs) {
// If post-boot update is still running, request that it exits early.
mExitPostBootUpdate.set(true);
mAbortIdleOptimization.set(false);
final long lowThreshold = getLowStorageThreshold();
new Thread("BackgroundDexOptService_IdleOptimization") {
@Override
public void run() {
for (String pkg : pkgs) {
if (mAbortIdleOptimization.get()) {
// JobScheduler requested an early abort.
return;
}
if (sFailedPackageNames.contains(pkg)) {
// Skip previously failing package
continue;
}
long usableSpace = dataDir.getUsableSpace();
if (usableSpace < lowThreshold) {
// Rather bail than completely fill up the disk.
Log.w(TAG, "Aborting background dex opt job due to low storage: " +
usableSpace);
break;
}
// Conservatively add package to the list of failing ones in case performDexOpt
// never returns.
synchronized (sFailedPackageNames) {
sFailedPackageNames.add(pkg);
}
// Optimize package if needed. Note that there can be no race between
// concurrent jobs because PackageDexOptimizer.performDexOpt is synchronized.
if (pm.performDexOpt(pkg,
/* checkProfiles */ true,
PackageManagerService.REASON_BACKGROUND_DEXOPT,
/* force */ false)) {
// Dexopt succeeded, remove package from the list of failing ones.
synchronized (sFailedPackageNames) {
sFailedPackageNames.remove(pkg);
}
}
}
// Ran to completion, so we abandon our timeslice and do not reschedule.
jobFinished(jobParams, /* reschedule */ false);
}
}.start();
return true;
}
@Override
public boolean onStartJob(JobParameters params) {
// NOTE: PackageManagerService.isStorageLow uses a different set of criteria from
// the checks above. This check is not "live" - the value is determined by a background
// restart with a period of ~1 minute.
PackageManagerService pm = (PackageManagerService)ServiceManager.getService("package");
if (pm.isStorageLow()) {
return false;
}
final ArraySet pkgs = pm.getOptimizablePackages();
if (pkgs == null || pkgs.isEmpty()) {
return false;
}
if (params.getJobId() == JOB_POST_BOOT_UPDATE) {
return runPostBootUpdate(params, pm, pkgs);
} else {
return runIdleOptimization(params, pm, pkgs);
}
}
@Override
public boolean onStopJob(JobParameters params) {
if (params.getJobId() == JOB_POST_BOOT_UPDATE) {
mAbortPostBootUpdate.set(true);
} else {
mAbortIdleOptimization.set(true);
}
return false;
}
}