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From "Salikh Zakirov (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-2320) [drlvm] Throw exception outside of HWE handler to avoid deadlocks on Windows XP
Date Fri, 24 Nov 2006 19:25:01 GMT
[drlvm] Throw exception outside of HWE handler to avoid deadlocks on Windows XP
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                 Key: HARMONY-2320
                 URL: http://issues.apache.org/jira/browse/HARMONY-2320
             Project: Harmony
          Issue Type: Sub-task
         Environment: Windows XP
            Reporter: Salikh Zakirov


The reason of hang of gc.LOS is deadlock on a thread suspension:
Assume thread A handles NPE:

A1) segfault occured
A2) grab "system hwe lock" and call vectored_exception_handler
A3) instantiate NullPointerException object
A4) set up throwing NullPointerExceptionObject in the register snapshot
A5) return from vectored_exception_handler release "system hwe lock"

Let's next assume that garbage collection was started exactly when thread A
was in progress of running NullPointerException constructor (A3). Then, thread A
will be suspended while still holding "system hwe lock".

Another thread B at that moment have just perfomed access to null pointer (B1),
and then it is blocked on a "system hwe lock" (B2),

Since this lock is system and not known to Thread Manager, the thread C which tries to start
garbage
collection and so requested suspension of all threads, and then waits forever for thread B
to reach a safepoint,
while B is waiting for thread A to release "system hwe lock", and thread A was already suspended
and waits
for thread C to resume it.

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