branch master updated: Avoid fiber deadlocks

[Christopher Baines]

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cbaines pushed a commit to branch master
in repository data-service.

The following commit(s) were added to refs/heads/master by this push:
     new 96b65f1  Avoid fiber deadlocks
96b65f1 is described below

commit 96b65f16fb2a6f5d568d7709a86e2307ef70fe0f
Author: Christopher Baines <mail@cbaines.net>
AuthorDate: Sun Oct 4 10:18:53 2020 +0100

    Avoid fiber deadlocks
    
    Channels don't represent some channel on which messages travel, at least 
not a
    very long one because it can't accommodate any messages. They simply 
represent
    a direct exchange of the message between a sender and receiver. Because of
    this, put-message blocks the fiber, and if all the threads on the other end
    are waiting for replies to be received, then you have a deadlock.
    
    To avoid this situation, spawn new fibers to send the messages. I think this
    works at least, although I'm unsure how sensible it is.
---
 guix-data-service/utils.scm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/guix-data-service/utils.scm b/guix-data-service/utils.scm
index 855c819..c50cb64 100644
--- a/guix-data-service/utils.scm
+++ b/guix-data-service/utils.scm
@@ -99,7 +99,9 @@
 (define (defer-to-thread-pool-channel thunk)
   (make-thread-pool-channel!)
   (let ((reply (make-channel)))
-    (put-message %thread-pool-channel (cons reply thunk))
+    (spawn-fiber
+     (lambda ()
+       (put-message %thread-pool-channel (cons reply thunk))))
     reply))
 
 (define (fetch-result-of-defered-thunk reply-channel)