关闭sqlite数据库时发生死锁

Question

我正在研究我的项目中的间歇性ANR。当后台有许多对数据库的请求，用户单击按钮，数据库作为注销的一部分被关闭时，就会发生这种情况。我使用的是saferoom和rx-java2。

这是一些来自测试项目的代码，我试图在其中重现问题。(重现约30%的时间)：

class MainActivity : AppCompatActivity() {

    lateinit var db: TestDb
    private val disposables = CompositeDisposable()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        openStorage("password")

        val d = Observable.interval(100, TimeUnit.MICROSECONDS)
            .map { db.testDao().insert(TestEntity()) }
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe({ status.text = "WRITING" }, {})
        disposables.add(d)

        closeDbButton.setOnClickListener {
            disposables.clear()
            db.close()
            status.text = "DB CLOSED"
        }
    }

    @Synchronized
    fun openStorage(storageSecret: String) {
        val factory = SafeHelperFactory(storageSecret.toCharArray())
        db = Room.databaseBuilder(this, TestDb::class.java, TestDb.DATABASE_NAME)
            .openHelperFactory(factory)
            .build()
    }
}

正如你所看到的，为了模拟这个问题，我试图在循环中访问数据库，同时关闭数据库。即使我在关闭前处理了写入链，死锁还是发生了，应用程序冻结了。

我还尝试分析了线程转储：

"main" prio=5 tid=1 Waiting
  | group="main" sCount=1 dsCount=0 flags=1 obj=0x727565f0 self=0x7b42cbea00
  | sysTid=24431 nice=-10 cgrp=default sched=0/0 handle=0x7bc78e99a8
  | state=S schedstat=( 3718987857 647207377 6247 ) utm=336 stm=34 core=3 HZ=100
  | stack=0x7fd4c9a000-0x7fd4c9c000 stackSize=8MB
  | held mutexes=
  at java.lang.Object.wait(Native method)
  - waiting on <0x017bb93d> (a java.lang.Object)
  at java.lang.Thread.parkFor$(Thread.java:2137)
  - locked <0x017bb93d> (a java.lang.Object)
  at sun.misc.Unsafe.park(Unsafe.java:358)
  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:190)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:868)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:900)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1223)
  at java.util.concurrent.locks.ReentrantLock$FairSync.lock(ReentrantLock.java:225)
  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:286)
  at net.sqlcipher.database.SQLiteDatabase.lock(SQLiteDatabase.java:553)
  at net.sqlcipher.database.SQLiteDatabase.close(SQLiteDatabase.java:1284)
  at net.sqlcipher.database.SQLiteOpenHelper.close(SQLiteOpenHelper.java:272)
  - locked <0x064ca532> (a com.commonsware.cwac.saferoom.Helper$1)
  at com.commonsware.cwac.saferoom.Helper$OpenHelper.close(Helper.java:202)
  - locked <0x064ca532> (a com.commonsware.cwac.saferoom.Helper$1)
  at com.commonsware.cwac.saferoom.Helper.close(Helper.java:146)
  at androidx.room.RoomDatabase.close(RoomDatabase.java:189)
  at com.company.deadlocktest.MainActivity$onCreate$1.onClick(MainActivity.kt:38)
  at android.view.View.performClick(View.java:6294)
  at android.view.View$PerformClick.run(View.java:24770)
  at android.os.Handler.handleCallback(Handler.java:790)
  at android.os.Handler.dispatchMessage(Handler.java:99)
  at android.os.Looper.loop(Looper.java:164)
  at android.app.ActivityThread.main(ActivityThread.java:6494)
  at java.lang.reflect.Method.invoke(Native method)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)


"RxComputationThreadPool-1" daemon prio=5 tid=15 Blocked
  | group="main" sCount=1 dsCount=0 flags=1 obj=0x12fc0610 self=0x7b3a839c00
  | sysTid=24450 nice=0 cgrp=default sched=0/0 handle=0x7b2c5384f0
  | state=S schedstat=( 2462204096 250602566 3746 ) utm=209 stm=36 core=1 HZ=100
  | stack=0x7b2c436000-0x7b2c438000 stackSize=1037KB
  | held mutexes=
  at net.sqlcipher.database.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:-1)
  - waiting to lock <0x064ca532> (a com.commonsware.cwac.saferoom.Helper$1) held by thread 1
  at com.commonsware.cwac.saferoom.Helper$OpenHelper.getWritableSupportDatabase(Helper.java:158)
  at com.commonsware.cwac.saferoom.Helper.getWritableDatabase(Helper.java:120)
  at androidx.room.RoomDatabase.setTransactionSuccessful(RoomDatabase.java:286)
  at com.company.deadlocktest.TestDao_Impl.insert(TestDao_Impl.java:49)
  at com.company.deadlocktest.MainActivity$onCreate$d$1.apply(MainActivity.kt:30)
  at com.company.deadlocktest.MainActivity$onCreate$d$1.apply(MainActivity.kt:18)
  at io.reactivex.internal.operators.observable.ObservableMap$MapObserver.onNext(ObservableMap.java:59)
  at io.reactivex.internal.operators.observable.ObservableInterval$IntervalObserver.run(ObservableInterval.java:83)
  at io.reactivex.internal.schedulers.ScheduledDirectPeriodicTask.run(ScheduledDirectPeriodicTask.java:38)
  at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:457)
  at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:307)
  at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:302)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
  at java.lang.Thread.run(Thread.java:764)

正如您所看到的，Rx线程被锁阻塞，由主线程(<0x064ca532> com.commonsware.cwac.saferoom.Helper$1)获取，主线程处于等待状态。

所以我正在尝试找出是否有办法避免这个问题，或者这是saferoom / sqlcipher中的某种bug。

Answer 1

我不是RxJava专家，但我不认为clear()的线程化效果会立即发生。

就解决方法而言，不要在主应用程序线程上调用close()。通常，我们根本不close()，因为我们永远不知道什么时候是好时机，考虑到应用程序中正在发生的一切。如果您真的想使用close()，那么可以在用于数据库访问的Schedulers.io()线程上执行此操作。