一、使用严格模式：
微信图片_20180525114217.png
StrictMode严苛模式，是Android提供的一种运行时检测机制，一般用来检测在主线程做一些耗时动作，比如IO读写、数据库操作、Sp操作、Activity泄露、未关闭的Closable对象泄露等，以减少发生ANR等。严格模式主要有2个策略：一个是线程策略，即TreadPolicy是针对一个具体的线程，另一个是VM策略，即VmPolicy，是针对虚拟机的所有对象。
当然可以添加Penalty(惩罚)，一般我们都是用来打印日志、绘制红框等。
二、严格模式中是如何去检测，在哪个地方有注入StrictMode的代码：
在源码中可以直接植入StrictMode的检查代码、也可以植入代码是BlockGuard和CloseGuard的代码。
我们先看下UML：
2.png
1、BlockGuard:
public final class StrictMode {
public static void setThreadPolicy(final ThreadPolicy policy) {
setThreadPolicyMask(policy.mask);
}
private static void setThreadPolicyMask(final int policyMask) {
setBlockGuardPolicy(policyMask);
Binder.setThreadStrictModePolicy(policyMask);
}
// Sets the policy in Dalvik/libcore (BlockGuard)
private static void setBlockGuardPolicy(final int policyMask) {
if (policyMask == 0) {
BlockGuard.setThreadPolicy(BlockGuard.LAX_POLICY);
return;
}
final BlockGuard.Policy policy = BlockGuard.getThreadPolicy();
final AndroidBlockGuardPolicy androidPolicy;
if (policy instanceof AndroidBlockGuardPolicy) {
androidPolicy = (AndroidBlockGuardPolicy) policy;
} else {
androidPolicy = threadAndroidPolicy.get();
BlockGuard.setThreadPolicy(androidPolicy);
}
androidPolicy.setPolicyMask(policyMask);
}
}
其中在setBlockGuardPolicy(policyMask)把相应的AndroidBlockGuardPolicy设置到BlockGuard类，
并且Binder.setThreadStrictModePolicy()是Native层，当进程A发起跨进程调用进入到进程B后，进程B中的违规异常也是会通过Binder再传回进程A中。
2、CloseGuard：
public final class StrictMode {
public static void setVmPolicy(final VmPolicy policy) {
synchronized (StrictMode.class) {
sVmPolicy = policy;
sVmPolicyMask = policy.mask;
setCloseGuardEnabled(vmClosableObjectLeaksEnabled());
...
}
}
private static void setCloseGuardEnabled(boolean enabled) {
if (!(CloseGuard.getReporter() instanceof AndroidCloseGuardReporter)) {
CloseGuard.setReporter(new AndroidCloseGuardReporter());
}
CloseGuard.setEnabled(enabled);
}
}
函数setCloseGuardEnabled注入AndroidCloseGuardReporter后，在Android很多代码都会使用CloseGuard.get()获取全局的CloseGuard进行检测输出打印日志出来。
三、植入严格模式检测的代码：
1）、FileInPutStream中：读写file时，有BlockGuard检测UI线程操作文件，有CloseGuard检测报告的未关闭文件等。
class FileInputStream extends InputStream{
private final CloseGuard guard = CloseGuard.get();
public FileInputStream(File file) throws FileNotFoundException {
...
BlockGuard.getThreadPolicy().onReadFromDisk();
open(name);
guard.open("close");
}
public void close() throws IOException {
...
guard.close();
...
}
protected void finalize() throws IOException {
if (guard != null) {
guard.warnIfOpen();
}
if ((fd != null) && (fd != FileDescriptor.in)) {
close();
}
}
}
2）、SQLiteCursor ：在SQLiteCursor对象销毁时，会对Cursor是否关闭进行判断相应向StrictMode报告
public class SQLiteCursor extends AbstractWindowedCursor {
public SQLiteCursor(SQLiteCursorDriver driver, String editTable, SQLiteQuery query) {
...
if (StrictMode.vmSqliteObjectLeaksEnabled()) {
mStackTrace = new DatabaseObjectNotClosedException().fillInStackTrace();
} else {
mStackTrace = null;
}
...
}
protected void finalize() {
try {
if (mWindow != null) {
if (mStackTrace != null) {
String sql = mQuery.getSql();
int len = sql.length();
StrictMode.onSqliteObjectLeaked(
"Finalizing a Cursor that has not been deactivated or closed. " +
"database = " + mQuery.getDatabase().getLabel() +
", table = " + mEditTable +
", query = " + sql.substring(0, (len > 1000) ? 1000 : len),
mStackTrace);
}
close();
}
} finally {
super.finalize();
}
}
}
3）、Activity泄露，在ActivityThread中Activity的启动和销毁都有植入StrictMode相应的代码去检测Activity的引用计数，来判断是否有泄露，在StrictMode.decrementExpectedActivityCount(activityClass);会手动System.gc();
public final class ActivityThread {
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
...
} catch (Exception e) {
}
...
return activity;
}
private ActivityClientRecord performDestroyActivity(IBinder token, boolean finishing,
int configChanges, boolean getNonConfigInstance) {
...
try {
r.activity.mCalled = false;
mInstrumentation.callActivityOnDestroy(r.activity);
...
} catch (Exception e) {
}
}
StrictMode.decrementExpectedActivityCount(activityClass);
return r;
}
}
4）、SharedPreferencesImpl 中getString、getInt等也植入了BlockGuard
final class SharedPreferencesImpl implements SharedPreferences {
@Nullable
public String getString(String key, @Nullable String defValue) {
synchronized (this) {
awaitLoadedLocked();
...
}
}
@Nullable
public Set<String> getStringSet(String key, @Nullable Set<String> defValues) {
synchronized (this) {
awaitLoadedLocked();
...
}
}
public int getInt(String key, int defValue) {
synchronized (this) {
awaitLoadedLocked();
...
}
}
private void awaitLoadedLocked() {
if (!mLoaded) {
// Raise an explicit StrictMode onReadFromDisk for this
// thread, since the real read will be in a different
// thread and otherwise ignored by StrictMode.
BlockGuard.getThreadPolicy().onReadFromDisk();
}
while (!mLoaded) {
try {
wait();
} catch (InterruptedException unused) {
}
}
}
}
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