IssueTracker

Component used: WorkManager
Version used: 1.0.1
Devices/Android versions reproduced on: different Samsung Galaxy devices running Android 8 and 9

I have received deadlock reports like this:

"main" prio=5 tid=1 Blocked
  | group="main" sCount=1 dsCount=0 flags=1 obj=0x76790a58 self=0x7d81014c00
  | sysTid=27874 nice=0 cgrp=default sched=0/0 handle=0x7e07c1a560
  | state=S schedstat=( 1835900780 7285545518 5958 ) utm=82 stm=100 core=1 HZ=100
  | stack=0x7febcdd000-0x7febcdf000 stackSize=8MB
  | held mutexes=
  at androidx.work.impl.constraints.trackers.ConstraintTracker.removeListener (ConstraintTracker.java:77)
- waiting to lock <0x08a4f10d> (a java.lang.Object) held by thread 13 // ConstraintTracker.mLock
  at androidx.work.impl.constraints.controllers.ConstraintController.replace (ConstraintController.java:98)
  at androidx.work.impl.constraints.WorkConstraintsTracker.replace (WorkConstraintsTracker.java:99)
- locked <0x0cbac8c2> (a java.lang.Object) // WorkConstrainsTracker.mLock
  at androidx.work.impl.background.greedy.GreedyScheduler.removeConstraintTrackingFor (GreedyScheduler.java:153)
- locked <0x0cbec6d3> (a java.lang.Object) // GreedyScheduler.mLock
  at androidx.work.impl.background.greedy.GreedyScheduler.onExecuted (GreedyScheduler.java:141)
  at androidx.work.impl.Processor.onExecuted (Processor.java:230)
- locked <0x08012210> (a java.lang.Object)
  at androidx.work.impl.Processor$FutureListener.run (Processor.java:263)
  at android.os.Handler.handleCallback (Handler.java:873)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at android.os.Looper.loop (Looper.java:214)
  at android.app.ActivityThread.main (ActivityThread.java:7032)
  at java.lang.reflect.Method.invoke (Method.java)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:494)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:965)
"ConnectivityThread" tid=13 Blocked
"ConnectivityThread" prio=5 tid=13 Blocked
  | group="main" sCount=1 dsCount=0 flags=1 obj=0x12fc0770 self=0x7d7ab86800
  | sysTid=27897 nice=0 cgrp=default sched=0/0 handle=0x7d684114f0
  | state=S schedstat=( 247567475 11539483672 1368 ) utm=16 stm=7 core=2 HZ=100
  | stack=0x7d6830e000-0x7d68310000 stackSize=1041KB
  | held mutexes=
  at androidx.work.impl.a.d.c (SourceFile:157) // synchronized (mLock)
- waiting to lock <0x0cbac8c2> (a java.lang.Object) held by thread 1 // trying to lock WorkConstraintsTracker.mLock
  at androidx.work.impl.a.a.c.b (SourceFile:133) ConstraintController: mCallback.onConstraintNotMet(mMatchingWorkSpecIds);
  at androidx.work.impl.a.a.c.a (SourceFile:142) ConstraintController: updateCallback();
  at androidx.work.impl.a.b.d.a (SourceFile:103) listener.onConstraintChanged(mCurrentState);
- locked <0x08a4f10d> (a java.lang.Object) (ConstraintTracker.mLock)
  at androidx.work.impl.a.b.e$b.onCapabilitiesChanged (SourceFile:149) (NetworkStateTracker)
  at android.net.ConnectivityManager$CallbackHandler.handleMessage (ConnectivityManager.java:3331)
  at android.os.Handler.dispatchMessage (Handler.java:106)
  at android.os.Looper.loop (Looper.java:214)
  at android.os.HandlerThread.run (HandlerThread.java:65)


I have written after the lines what is happening there.

The GreedyScheduler has finished executing and onExecuted is called. This tries to remove the workSpecId from the mConstrainedWorkSpecs list. After removing it it calls mWorkConstraintsTracker.replace to send the new list to the WorkContraintsTracker. This causes a lock of WorkConstraintsTracker.mLock and a call to ConstraintController.replace. This calls ConstraintController.removeListener which tries to lock ConstraintController.mLock but fails/deadlocks. So as you can see it has first locked WorkConstraintsTracker.mLock and then it tries to lock ConstraintController.mLock.

As you can see now the other thread does the opposite, which leads to the deadlock: The WorkManager receives a "onCapabilitiesChanges" message and locks ConstraintTracker.mLock. Then it tries to call onConstraintNotMet but it cannot lock WorkConstraintsTracker.mLock, because it is already locked by the upper thread.

So there is a deadlock because both functions are running at the same time and are locking the locks in opposite order. Can you please fix it? Or did I make a mistake somewhere?

(BTW I am only using WorkManager.getInstance, I am not calling "initialize").

Thank you very much!