branch master updated: utils: Handle errors in worker threads.

[Christopher Baines]

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cbaines pushed a commit to branch master
in repository guix-cuirass.

The following commit(s) were added to refs/heads/master by this push:
     new bb22518  utils: Handle errors in worker threads.
bb22518 is described below

commit bb225189fd56d89ec8be926dda269295ccbfe918
Author: Christopher Baines <address@hidden>
AuthorDate: Mon Feb 3 12:58:22 2020 +0100

    utils: Handle errors in worker threads.
    
    Previously, if an error occurred, the worker fiber simply never sends a
    reply. In the case of HTTP requests to Cuirass, where an exception occurs 
when
    performing a database query, the fiber handling the request blocks as it 
never
    gets a response. I think that this has the potential to cause the process to
    hit file descriptor limits, as the connections are never responded to.
    
    This is fixed by responding with the details of the exception, and then
    throwing it within the fiber that made the call.
    
    * src/cuirass/utils.scm (make-worker-thread-channel): Catch exceptions when
    calling proc.
    (call-with-worker-thread): Handle receiving exceptions from the worker 
thread.
---
 src/cuirass/utils.scm | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/cuirass/utils.scm b/src/cuirass/utils.scm
index f3ba18d..0bcbb35 100644
--- a/src/cuirass/utils.scm
+++ b/src/cuirass/utils.scm
@@ -114,7 +114,12 @@ arguments of the worker thread procedure."
                 (let loop ()
                   (match (get-message channel)
                     (((? channel? reply) . (? procedure? proc))
-                     (put-message reply (apply proc args))))
+                     (put-message reply
+                                  (catch #t
+                                    (lambda ()
+                                      (apply proc args))
+                                    (lambda (key . args)
+                                      (cons* 'worker-thread-error key 
args))))))
                   (loop)))))))
        (iota parallelism))
       channel)))
@@ -127,7 +132,10 @@ If already in the worker thread, call PROC immediately."
         (apply proc args)
         (let ((reply (make-channel)))
           (put-message channel (cons reply proc))
-          (get-message reply)))))
+          (match (get-message reply)
+            (('worker-thread-error key args ...)
+             (apply throw key args))
+            (result result))))))
 
 (define-syntax-rule (with-worker-thread channel (vars ...) exp ...)
   "Evaluate EXP... in the worker thread corresponding to CHANNEL.