Ayende @ Rahien

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My name is Ayende Rahien
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ChallengeFind the deadlock


Okay, there isn't much of a challenge here, but it is worth point out nevertheless:

image image

More posts in "Challenge" series:

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  2. (26 Sep 2013) Spot the bug
  3. (27 May 2013) The problem of locking down tasks…
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  5. (23 Aug 2011) Recent Comments with Future Posts
  6. (02 Aug 2011) Modifying execution approaches
  7. (29 Apr 2011) Stop the leaks
  8. (23 Dec 2010) This code should never hit production
  9. (17 Dec 2010) Your own ThreadLocal
  10. (03 Dec 2010) Querying relative information with RavenDB
  11. (29 Jun 2010) Find the bug
  12. (23 Jun 2010) Dynamically dynamic
  13. (28 Apr 2010) What killed the application?
  14. (19 Mar 2010) What does this code do?
  15. (04 Mar 2010) Robust enumeration over external code
  16. (16 Feb 2010) Premature optimization, and all of that…
  17. (12 Feb 2010) Efficient querying
  18. (10 Feb 2010) Find the resource leak
  19. (21 Oct 2009) Can you spot the bug?
  20. (18 Oct 2009) Why is this wrong?
  21. (17 Oct 2009) Write the check in comment
  22. (15 Sep 2009) NH Prof Exporting Reports
  23. (02 Sep 2009) The lazy loaded inheritance many to one association OR/M conundrum
  24. (01 Sep 2009) Why isn’t select broken?
  25. (06 Aug 2009) Find the bug fixes
  26. (26 May 2009) Find the bug
  27. (14 May 2009) multi threaded test failure
  28. (11 May 2009) The regex that doesn’t match
  29. (24 Mar 2009) probability based selection
  30. (13 Mar 2009) C# Rewriting
  31. (18 Feb 2009) write a self extracting program
  32. (04 Sep 2008) Don't stop with the first DSL abstraction
  33. (02 Aug 2008) What is the problem?
  34. (28 Jul 2008) What does this code do?
  35. (26 Jul 2008) Find the bug fix
  36. (05 Jul 2008) Find the deadlock
  37. (03 Jul 2008) Find the bug
  38. (02 Jul 2008) What is wrong with this code
  39. (05 Jun 2008) why did the tests fail?
  40. (27 May 2008) Striving for better syntax
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Comments

Aditya Caprihan

If ‘ReleaseEnv’ is being executed on thread T1 and ‘AcquireEnv’ is being executed on thread T2 and both methods have been passed the same ‘fullPath’ and 'container.Release' returns 'true', there will be a deadlock in the following scenario:

T1 has a lock on ‘container’ and it releases its read lock and gets queued for a write lock. T2 already has a read lock and is now waiting to get a lock on ‘container’ (which T1 has a lock on). Since T1 is waiting for T2 to release its read lock and T2 is waiting on T1 to release the lock on ‘container’, both threads are waiting on each other and we have a deadlock.

Omer Mor

looks easy:

If T1 & T2 both enter ReleaseEnv() with an existing path, they'll both acquire read-lock, T1 will enter the monitor, and will try to upgrade to write-lock, but will block until T2 releases its read-lock.

Meanwhile T2 will block until T1 will leave the monitor.

So:

T1 waits for T2 (can't upgrade to writer),

T2 waits for T1 (can't enter monitor),

ergo: deadlock.

Omer.

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