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diff --git a/src/pl-thread.c b/src/pl-thread.c
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index 19c2484..9feaf0b 100644
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--- a/src/pl-thread.c
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+++ b/src/pl-thread.c
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@@ -2773,9 +2773,11 @@ running. The thread may pick a message containing an atom from the
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queue, which now has not been marked and is no longer part of the
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queue, so it isn't marked in the queue either.
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-Note that we only need this for queues that are not associated to
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-threads. Those associated with a thread mark both the stacks and the
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-queue in one pass, marking the atoms in either.
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+Originally, I thought we only need this for queues that are not
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+associated to threads. Those associated with a thread mark both the
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+stacks and the queue in one pass, marking the atoms in either. However,
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+we also need to lock to avoid get_message() destroying the record while
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+markAtomsMessageQueue() scans it. This fixes the reopened Bug#142.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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static int
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@@ -2827,13 +2829,10 @@ get_message(message_queue *queue, term_t msg, struct timespec *deadline ARG_LD)
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if ( rc )
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{ DEBUG(MSG_QUEUE, Sdprintf("%d: match\n", PL_thread_self()));
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- if (GD->atoms.gc_active)
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- markAtomsRecord(msgp->message);
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+ if (GD->atoms.gc_active)
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+ markAtomsRecord(msgp->message);
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-#ifdef O_ATOMGC
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- if ( queue->type == QTYPE_QUEUE )
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- simpleMutexLock(&queue->gc_mutex);
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-#endif
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+ simpleMutexLock(&queue->gc_mutex); /* see (*) */
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if ( prev )
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{ if ( !(prev->next = msgp->next) )
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queue->tail = prev;
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@@ -2841,10 +2840,8 @@ get_message(message_queue *queue, term_t msg, struct timespec *deadline ARG_LD)
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{ if ( !(queue->head = msgp->next) )
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queue->tail = NULL;
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}
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-#ifdef O_ATOMGC
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- if ( queue->type == QTYPE_QUEUE )
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- simpleMutexUnlock(&queue->gc_mutex);
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-#endif
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+ simpleMutexUnlock(&queue->gc_mutex);
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+
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free_thread_message(msgp);
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queue->size--;
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if ( queue->wait_for_drain )
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