Avoid using select and use poll instead

I don't trust select, as I think I'm seeing it make blocking read calls. I
don't know if that's coming from here, but better to just avoid it.

1 files changed, 3 insertions, 7 deletions

diff --git a/guix-build-coordinator/utils/fibers.scm b/guix-build-coordinator/utils/fibers.scm
index 293429c..2c7307f 100644
--- a/guix-build-coordinator/utils/fibers.scm
+++ b/guix-build-coordinator/utils/fibers.scm
@@ -447,20 +447,16 @@ If already in the worker thread, call PROC immediately."
 
 (define (readable? port)
   "Test if PORT is writable."
-  (match (select (vector port) #() #() 0)
-    ((#() #() #()) #f)
-    ((#(_) #() #()) #t)))
+  (= 1 (port-poll port "r" 0)))
 
 (define (writable? port)
   "Test if PORT is writable."
-  (match (select #() (vector port) #() 0)
-    ((#() #() #()) #f)
-    ((#() #(_) #()) #t)))
+  (= 1 (port-poll port "w" 0)))
 
 (define (make-wait-operation ready? schedule-when-ready port port-ready-fd this-procedure)
   (make-base-operation #f
                        (lambda _
-                         (and (ready? (port-ready-fd port)) values))
+                         (and (ready? port) values))
                        (lambda (flag sched resume)
                          (define (commit)
                            (match (atomic-box-compare-and-swap! flag 'W 'S)