From: Matt Birkholz <puck@birchwood-abbey.net>
Date: Sun, 31 Jan 2016 01:10:37 +0000 (-0700)
Subject: Fix try-lock-thread-mutex to work when there is no current thread.
X-Git-Tag: mit-scheme-pucked-9.2.12~371^2~4
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=eb547ca67c6ab282ba805fbb7e19826d32f940a7;p=mit-scheme.git

Fix try-lock-thread-mutex to work when there is no current thread.

GC daemons need to run when there is no current thread.  Try-lock-
thread-mutex was intended for their use.  They do not mind
occasionally skipping an opportunity to clean, including the rare
times when a GC interrupt occurs with no current thread -- in the
thread system of a quiescent world.

Try-lock-thread-mutex was signaling spurious deadlocks when GC daemons
ran with no current thread.  Free locks appeared to be owned by #F --
the current thread.
---

diff --git a/src/runtime/thread.scm b/src/runtime/thread.scm
index 442bbd8fb..744a382e6 100644
--- a/src/runtime/thread.scm
+++ b/src/runtime/thread.scm
@@ -1202,10 +1202,13 @@ USA.
   (without-interrupts
    (lambda ()
      (and (not (thread-mutex/owner mutex))
-	  (let ((thread (current-thread)))
-	    (set-thread-mutex/owner! mutex thread)
-	    (add-thread-mutex! thread mutex)
-	    #t)))))
+	  (let ((thread first-running-thread))
+	    ;; GC daemons may use this when there is no current thread.
+	    (and thread
+		 (begin
+		   (set-thread-mutex/owner! mutex thread)
+		   (add-thread-mutex! thread mutex)
+		   #t)))))))
 
 (define (with-thread-mutex-lock mutex thunk)
   (guarantee-thread-mutex mutex 'WITH-THREAD-MUTEX-LOCK)