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Report From: Delphi-BCB/RTL/Delphi/Thread support [ Add a report in this area ]

Report #: 17914

Status: Closed

(Pulled) TMultiReadExclusiveWriteSynchronizer can deadlock if calls to BeginRead are nested.

Project: Delphi

Build #: 5.0.5.56

Version: 5.0

Submitted By: John Kaster

Report Type: Crash / Data loss / Total failure

Date Reported: 8/11/1999 12:00:00 AM

Severity: Infrequently encountered problem

Last Updated: 3/20/2012 2:24:39 AM

Platform: All versions

Internal Tracking #: 68233

Resolution: Fixed (Resolution Comments)

Resolved in Build: : 10.0.2098.14501

Duplicate of: None

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Description

TMultiReadExclusiveWriteSynchronizer can deadlock if calls to BeginRead are nested.

Steps to Reproduce:

There seems to be a potential problem with how TMultiReadExclusiveWriteSynchronizer is implemented. If a thread tries to get a read lock (with BeginRead) twice and another thread tries to get a write lock, deadlocks can occur:
- Thread 1 calls BeginRead and gets a read lock
- Thread 2 calls BeginWrite, holds the FLock critical section, then waits INFINE on a signal that the last reader released its readlock
- Thread 1 calls BeginRead again. It waits for the FLock critical section. This is held by Thread 2, which is waiting for Thread 1 to continue...
- Deadlock...
- Run the attached project.
// Note that the ShowMessage is never reached because of the deadlock

Workarounds

None

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