每日一问 | 系统会随意删除App的缓存文件？

参考:frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java

/**

 * Blocking call to clear various types of cached data across the system
 * until the requested bytes are available.
 */
public void freeStorage(String volumeUuid, long bytes,
        @StorageManager.AllocateFlags int flags) throws IOException {
    final StorageManager storage = mInjector.getSystemService(StorageManager.class);
    final File file = storage.findPathForUuid(volumeUuid);
    if (file.getUsableSpace() >= bytes) return;

    if (mEnableFreeCacheV2) {
        final boolean internalVolume = Objects.equals(StorageManager.UUID_PRIVATE_INTERNAL,
                volumeUuid);
        final boolean aggressive = (flags & StorageManager.FLAG_ALLOCATE_AGGRESSIVE) != 0;

        // 1. Pre-flight to determine if we have any chance to succeed
        // 2. Consider preloaded data (after 1w honeymoon, unless aggressive)
        if (internalVolume && (aggressive || SystemProperties
                .getBoolean("persist.sys.preloads.file_cache_expired", false))) {
            deletePreloadsFileCache();
            if (file.getUsableSpace() >= bytes) return;
        }

        // 3. Consider parsed APK data (aggressive only)
        if (internalVolume && aggressive) {
            FileUtils.deleteContents(mCacheDir);
            if (file.getUsableSpace() >= bytes) return;
        }

        // 4. Consider cached app data (above quotas)
        synchronized (mInstallLock) {
            try {
                mInstaller.freeCache(volumeUuid, bytes, Installer.FLAG_FREE_CACHE_V2);
            } catch (InstallerException ignored) {
            }
        }
        if (file.getUsableSpace() >= bytes) return;

        Computer computer = snapshotComputer();
        // 5. Consider shared libraries with refcount=0 and age>min cache period
        if (internalVolume && mSharedLibraries.pruneUnusedStaticSharedLibraries(computer, bytes,
                android.provider.Settings.Global.getLong(mContext.getContentResolver(),
                        Global.UNUSED_STATIC_SHARED_LIB_MIN_CACHE_PERIOD,
                        FREE_STORAGE_UNUSED_STATIC_SHARED_LIB_MIN_CACHE_PERIOD))) {
            return;
        }

        // 6. Consider dexopt output (aggressive only)
        // TODO: Implement

        // 7. Consider installed instant apps unused longer than min cache period
        if (internalVolume) {
            if (mInstantAppRegistry.pruneInstalledInstantApps(computer, bytes,
                    android.provider.Settings.Global.getLong(
                            mContext.getContentResolver(),
                            Global.INSTALLED_INSTANT_APP_MIN_CACHE_PERIOD,
                            InstantAppRegistry
                                    .DEFAULT_INSTALLED_INSTANT_APP_MIN_CACHE_PERIOD))) {
                return;
            }
        }

        // 8. Consider cached app data (below quotas)
        synchronized (mInstallLock) {
            try {
                mInstaller.freeCache(volumeUuid, bytes,
                        Installer.FLAG_FREE_CACHE_V2 | Installer.FLAG_FREE_CACHE_V2_DEFY_QUOTA);
            } catch (InstallerException ignored) {
            }
        }
        if (file.getUsableSpace() >= bytes) return;

        // 9. Consider DropBox entries
        // TODO: Implement

        // 10. Consider instant meta-data (uninstalled apps) older that min cache period
        if (internalVolume) {
            if (mInstantAppRegistry.pruneUninstalledInstantApps(computer, bytes,
                    android.provider.Settings.Global.getLong(
                            mContext.getContentResolver(),
                            Global.UNINSTALLED_INSTANT_APP_MIN_CACHE_PERIOD,
                            InstantAppRegistry
                                    .DEFAULT_UNINSTALLED_INSTANT_APP_MIN_CACHE_PERIOD))) {
                return;
            }
        }

        // 11. Free storage service cache
        StorageManagerInternal smInternal =
                mInjector.getLocalService(StorageManagerInternal.class);
        long freeBytesRequired = bytes - file.getUsableSpace();
        if (freeBytesRequired > 0) {
            smInternal.freeCache(volumeUuid, freeBytesRequired);
        }

        // 12. Clear temp install session files
        mInstallerService.freeStageDirs(volumeUuid);
    } else {
        synchronized (mInstallLock) {
            try {
                mInstaller.freeCache(volumeUuid, bytes, 0);
            } catch (InstallerException ignored) {
            }
        }
    }
    if (file.getUsableSpace() >= bytes) return;

    throw new IOException("Failed to free " + bytes + " on storage device at " + file);
}