Android 系统缓存扫描与清理方法分析

private void refreshSizeInfo() {
    if (mAppEntry.size == ApplicationsState.SIZE_INVALID
            || mAppEntry.size == ApplicationsState.SIZE_UNKNOWN) {
        ......
    } else {
        ......
        long cacheSize = mAppEntry.cacheSize + mAppEntry.externalCacheSize;
        if (mLastCacheSize != cacheSize) {
            mLastCacheSize = cacheSize;
            mCacheSize.setText(getSizeStr(cacheSize));
        }
        ......
    }
}

private boolean refreshUi() {
    ......
    mAppEntry = mState.getEntry(packageName);
    ......
}

AppEntry getEntry(String packageName) {
    ......
            for (int i=0; i<mApplications.size(); i++) {
                ApplicationInfo info = mApplications.get(i);
                if (packageName.equals(info.packageName)) {
                    entry = getEntryLocked(info);
                    break;
                }
            }
    .......
}

void addPackage(String pkgName) {
    try {
        synchronized (mEntriesMap) {
            ......
            ApplicationInfo info = mPm.getApplicationInfo(pkgName,
                    PackageManager.GET_UNINSTALLED_PACKAGES |
                    PackageManager.GET_DISABLED_COMPONENTS);
            mApplications.add(info);
            if (!mBackgroundHandler.hasMessages(BackgroundHandler.MSG_LOAD_ENTRIES)) {
                mBackgroundHandler.sendEmptyMessage(BackgroundHandler.MSG_LOAD_ENTRIES);
            }
            ......
        }
    } catch (NameNotFoundException e) {
    }
}

class BackgroundHandler extends Handler {
    ......
    @Override
    public void handleMessage(Message msg) {
        ......
        switch (msg.what) {
            ......
            case MSG_LOAD_ENTRIES: {
                ......
                if (numDone >= 6) {
                    ......
                } else {
                    sendEmptyMessage(MSG_LOAD_ICONS);
                }
            } break;
            case MSG_LOAD_ICONS: {
                ......
                if (numDone >= 2) {
                    ......
                } else {
                    sendEmptyMessage(MSG_LOAD_SIZES);
                }
            } break;
            case MSG_LOAD_SIZES: {
                synchronized (mEntriesMap) {
                    ......
                                mPm.getPackageSizeInfo(mCurComputingSizePkg, mStatsObserver);
                    ......
                }
            } break;
        }
    }
    ......
}

public class PackageManagerService extends IPackageManager.Stub {
    ......
    public void getPackageSizeInfo(final String packageName,
            final IPackageStatsObserver observer) {
        ......
        Message msg = mHandler.obtainMessage(INIT_COPY);
        msg.obj = new MeasureParams(stats, observer);
        mHandler.sendMessage(msg);
    }
    ......
}

class PackageHandler extends Handler {
    private boolean mBound = false;
    ......
    public void handleMessage(Message msg) {
        ......
            doHandleMessage(msg);
        ......
    }

    void doHandleMessage(Message msg) {
        switch (msg.what) {
            case INIT_COPY: {
                ......
                if (!mBound) {
                    if (!connectToService()) {
                        ......
                    } else {
                        ......
                    }
                } else {
                    ......
                }
                break;
            }
            case MCS_BOUND: {
                ......
                        if (params.startCopy()) {
                            ......
                        }
                ......
                break;
            }
            ......
        }
    }
    ......
}

void handleStartCopy() throws RemoteException {
    synchronized (mInstallLock) {
        mSuccess = getPackageSizeInfoLI(mStats.packageName, mStats);
    }

    ......

    if (mounted) {
        final File externalCacheDir = Environment
                .getExternalStorageAppCacheDirectory(mStats.packageName);
        final long externalCacheSize = mContainerService
                .calculateDirectorySize(externalCacheDir.getPath());
        mStats.externalCacheSize = externalCacheSize;

        ......
    }
}

public class Environment {
    ......
    private static final File EXTERNAL_STORAGE_ANDROID_DATA_DIRECTORY = new File(new File(
            getDirectory("EXTERNAL_STORAGE", "/storage/sdcard0"), "Android"), "data");
    ......
    public static File getExternalStorageAppCacheDirectory(String packageName) {
        return new File(new File(EXTERNAL_STORAGE_ANDROID_DATA_DIRECTORY,
                packageName), "cache");
    }
    ......
}

private boolean getPackageSizeInfoLI(String packageName, PackageStats pStats) {
    ......
        int res = mInstaller.getSizeInfo(packageName, p.mPath, publicSrcDir,
                asecPath, pStats);
    ......
}

class Installer {
    ......
    private boolean connect() {
            ......
            LocalSocketAddress address = new LocalSocketAddress("installd",
                    LocalSocketAddress.Namespace.RESERVED);

            mSocket.connect(address);
            ......
    }
    ......
    private synchronized String transaction(String cmd) {
        if (!connect()) {
            ......
        }

        if (!writeCommand(cmd)) {
            ......
        }
        if (readReply()) {
            ......
            return s;
        } else {
            ......
        }
    }
    public int getSizeInfo(String pkgName, String apkPath, String fwdLockApkPath,
            String asecPath, PackageStats pStats) {
        StringBuilder builder = new StringBuilder("getsize");
        builder.append(' ');
        builder.append(pkgName);
        builder.append(' ');
        builder.append(apkPath);
        ......

        String s = transaction(builder.toString());
        String res[] = s.split(" ");

        ......
        try {
            ......
            pStats.cacheSize = Long.parseLong(res[3]);
            ......
        } catch (NumberFormatException e) {
            return -1;
        }
    }
    ......
}

int get_size(const char *pkgname, const char *apkpath,
             const char *fwdlock_apkpath, const char *asecpath,
             int64_t *_codesize, int64_t *_datasize, int64_t *_cachesize,
             int64_t* _asecsize)
{
    ......
    if (create_pkg_path(path, pkgname, PKG_DIR_POSTFIX, 0)) {
        goto done;
    }

    d = opendir(path);
    ......
    dfd = dirfd(d);
    ......
    while ((de = readdir(d))) {
        const char *name = de->d_name;

        if (de->d_type == DT_DIR) {
            ......
            subfd = openat(dfd, name, O_RDONLY | O_DIRECTORY);
            if (subfd >= 0) {
                int64_t size = calculate_dir_size(subfd);
                if (!strcmp(name,"lib")) {
                    codesize += size;
                } else if(!strcmp(name,"cache")) {
                    cachesize += size;
                } else {
                    datasize += size;
                }
            }
        } else {
            ......
        }
    }
    ......
}

int create_pkg_path(char path[PKG_PATH_MAX],
                    const char *pkgname,
                    const char *postfix,
                    uid_t persona)
{
    size_t uid_len;
    char* persona_prefix;
    if (persona == 0) {
        persona_prefix = PRIMARY_USER_PREFIX;
        uid_len = 0;
    } else {
        ......
    }

    const size_t prefix_len = android_data_dir.len + strlen(persona_prefix) + uid_len + 1 /*slash*/;
    char prefix[prefix_len + 1];

    char *dst = prefix;
    size_t dst_size = sizeof(prefix);

    if (append_and_increment(&dst, android_data_dir.path, &dst_size) < 0
            || append_and_increment(&dst, persona_prefix, &dst_size) < 0) {
        ALOGE("Error building prefix for APK path");
        return -1;
    }

    ......

    dir_rec_t dir;
    dir.path = prefix;
    dir.len = prefix_len;

    return create_pkg_path_in_dir(path, &dir, pkgname, postfix);
}

......
#define PRIMARY_USER_PREFIX    "data/"
......
#define PKG_DIR_POSTFIX        ""
......

int initialize_globals() {
    // Get the android data directory.
    if (get_path_from_env(&android_data_dir, "ANDROID_DATA") < 0) {
        return -1;
    }
    ......
}

shell@aries:/ $ echo $ANDROID_DATA
/data

class BackgroundHandler extends Handler {
    ......
    final IPackageStatsObserver.Stub mStatsObserver = new IPackageStatsObserver.Stub() {
                public void onGetStatsCompleted(PackageStats stats, boolean succeeded) {
                    ......
                                    entry.cacheSize = stats.cacheSize;
                                    ......
                                    entry.externalCacheSize = stats.externalCacheSize;
                    ......
                }
            };
    ......
    @Override
    public void handleMessage(Message msg) {
        ......
        switch (msg.what) {
            ......
            case MSG_LOAD_SIZES: {
                synchronized (mEntriesMap) {
                    ......
                                mPm.getPackageSizeInfo(mCurComputingSizePkg, mStatsObserver);
                    ......
                }
            } break;
        }
    }
    ......
}

public class InstalledAppDetails extends Fragment
        implements View.OnClickListener, CompoundButton.OnCheckedChangeListener,
        ApplicationsState.Callbacks {
    ......
    private Button mClearCacheButton;
    ......
    class ClearCacheObserver extends IPackageDataObserver.Stub {
        public void onRemoveCompleted(final String packageName, final boolean succeeded) {
            final Message msg = mHandler.obtainMessage(CLEAR_CACHE);
            msg.arg1 = succeeded ? OP_SUCCESSFUL:OP_FAILED;
            mHandler.sendMessage(msg);
         }
     }
    ......
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        ......
        mClearCacheButton = (Button) view.findViewById(R.id.clear_cache_button);
        ......
    }
    ......
    private void refreshSizeInfo() {
        ......
        if (cacheSize <= 0) {
            mClearCacheButton.setEnabled(false);
        } else {
            mClearCacheButton.setEnabled(true);
            mClearCacheButton.setOnClickListener(this);
        }
    }
    ......
    public void onClick(View v) {
        ......
        } else if (v == mClearCacheButton) {
            // Lazy initialization of observer
            if (mClearCacheObserver == null) {
                mClearCacheObserver = new ClearCacheObserver();
            }
            mPm.deleteApplicationCacheFiles(packageName, mClearCacheObserver);
        }
        ......
    }

/**
 * Attempts to delete the cache files associated with an application.
 * Since this may take a little while, the result will
 * be posted back to the given observer.  A deletion will fail if the calling context
 * lacks the {@link android.Manifest.permission#DELETE_CACHE_FILES} permission, if the
 * named package cannot be found, or if the named package is a "system package".
 *
 * ......
 *
 * @hide
 */

<!-- Allows an application to delete cache files. -->
<permission android:name="android.permission.DELETE_CACHE_FILES"
    android:label="@string/permlab_deleteCacheFiles"
    android:description="@string/permdesc_deleteCacheFiles"
    android:protectionLevel="signature|system" />

/**
 * Free storage by deleting LRU sorted list of cache files across
 * all applications. If the currently available free storage
 * on the device is greater than or equal to the requested
 * free storage, no cache files are cleared. If the currently
 * available storage on the device is less than the requested
 * free storage, some or all of the cache files across
 * all applications are deleted (based on last accessed time)
 * to increase the free storage space on the device to
 * the requested value. There is no guarantee that clearing all
 * the cache files from all applications will clear up
 * enough storage to achieve the desired value.
 * @param freeStorageSize The number of bytes of storage to be
 * freed by the system. Say if freeStorageSize is XX,
 * and the current free storage is YY,
 * if XX is less than YY, just return. if not free XX-YY number
 * of bytes if possible.
 * @param observer call back used to notify when
 * the operation is completed
 *
 * @hide
 */
public abstract void freeStorageAndNotify(long freeStorageSize, IPackageDataObserver observer);

public class PackageManagerService extends IPackageManager.Stub {
    ......
    public void freeStorageAndNotify(final long freeStorageSize, final IPackageDataObserver observer) {
        mContext.enforceCallingOrSelfPermission(
                android.Manifest.permission.CLEAR_APP_CACHE, null);
        // Queue up an async operation since clearing cache may take a little while.
        mHandler.post(new Runnable() {
            public void run() {
                mHandler.removeCallbacks(this);
                int retCode = -1;
                retCode = mInstaller.freeCache(freeStorageSize);
                if (retCode < 0) {
                    Slog.w(TAG, "Couldn't clear application caches");
                }
                if (observer != null) {
                    try {
                        observer.onRemoveCompleted(null, (retCode >= 0));
                    } catch (RemoteException e) {
                        Slog.w(TAG, "RemoveException when invoking call back");
                    }
                }
            }
        });
    }
    ......
}

<!-- Allows an application to clear the caches of all installed
     applications on the device.  -->
<permission android:name="android.permission.CLEAR_APP_CACHE"
    android:permissionGroup="android.permission-group.SYSTEM_TOOLS"
    android:protectionLevel="dangerous"
    android:label="@string/permlab_clearAppCache"
    android:description="@string/permdesc_clearAppCache" />

int free_cache(int64_t free_size)
{
    ......
    char datadir[PKG_PATH_MAX];
    avail = disk_free();
    ......
    if (avail >= free_size) return 0;

    if (create_persona_path(datadir, 0)) { // /data/data
        ......
    }

    d = opendir(datadir);
    ......
    dfd = dirfd(d);

    while ((de = readdir(d))) {
        if (de->d_type != DT_DIR) continue;
        name = de->d_name;
        ......
        subfd = openat(dfd, name, O_RDONLY | O_DIRECTORY);
        if (subfd < 0) continue;

        delete_dir_contents_fd(subfd, "cache");
        close(subfd);

        avail = disk_free();
        if (avail >= free_size) {
            closedir(d);
            return 0;
        }
    }
    ......
}