From 0d23a6d374340f3f9a3b035f960abd39447e11c3 Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Fri, 24 Jan 2020 18:25:47 +0000
Subject: utils: Change critical section terminology to worker threads.

As far as I'm aware, it's necessary to use a separate thread for interacting
with SQLite as one of the threads used for fibers will be blocked while the
SQLite query is running.

This doesn't mean all queries have to be executed one at a time though,
providing the queries are executed outside the threads used by fibers, and a
single connection isn't used in multiple threads.

These changes start to move in this direction, first by just changing the
terminology.

* src/cuirass/base.scm (clear-build-queue, cancel-old-builds): Change
with-db-critical-section to with-db-worker-thread.
* src/cuirass/database.scm (with-db-critical-section): Rename syntax rule to
with-db-worker-thread.
(db-add-input, db-add-checkout, db-add-specification, db-remove-specification,
db-get-inputs, db-get-specification, db-add-evaluation,
db-set-evaluations-done, db-set-evaluation-done, db-add-derivation-output,
db-add-build, db-update-build-status!, db-get-output, db-get-outputs,
db-get-builds-by-search, db-get-builds, db-get-build derivation-or-id,
db-add-event, db-get-events, db-delete-events-with-ids-<=-to,
db-get-pending-derivations, db-get-checkouts, db-get-evaluations,
db-get-evaluations-build-summary, db-get-evaluations-id-max,
db-get-evaluation-summary, db-get-builds-query-min, db-get-builds-query-max,
db-get-builds-min, db-get-builds-max, db-get-evaluation-specification): Change
from using with-db-critical-section to
with-db-worker-thread.
(with-database): Change syntax rule to use make-worker-thread-channel,
renaming from make-critical-section.
* src/cuirass/utils.scm (%critical-section-args): Rename parameter to
%worker-thread-args.
(make-critical-section): Rename to make-worker-thread-channel, and adjust
parameter and docstring.
(call-with-critical-section): Rename to call-with-worker-thread and adjust
parameter.
(with-critical-section): Rename to with-worker-thread, and adjust to call
call-with-worker-thread.
* tests/database.scm (db-init): Use make-worker-thread-channel rather than
make-critical-section.
* tests/http.scm (db-init): Use make-worker-thread-channel rather than
make-critical-section.
---
 src/cuirass/utils.scm | 38 +++++++++++++++++---------------------
 1 file changed, 17 insertions(+), 21 deletions(-)

(limited to 'src/cuirass/utils.scm')

diff --git a/src/cuirass/utils.scm b/src/cuirass/utils.scm
index fe74b69..514899e 100644
--- a/src/cuirass/utils.scm
+++ b/src/cuirass/utils.scm
@@ -35,9 +35,9 @@
             define-enumeration
             unwind-protect
 
-            make-critical-section
-            call-with-critical-section
-            with-critical-section
+            make-worker-thread-channel
+            call-with-worker-thread
+            with-worker-thread
 
             %non-blocking
             non-blocking
@@ -96,21 +96,17 @@ delimited continuations and fibers."
         (conclusion)
         (apply throw args)))))
 
-(define %critical-section-args
+(define %worker-thread-args
   (make-parameter #f))
 
-(define (make-critical-section . args)
-  "Return a channel used to implement a critical section.  That channel can
-then be passed to 'join-critical-section', which will ensure sequential
-ordering.  ARGS are the arguments of the critical section.
-
-Critical sections are implemented by passing the procedure to execute to a
-dedicated thread."
+(define (make-worker-thread-channel . args)
+  "Return a channel used to offload work to a dedicated thread.  ARGS are the
+arguments of the worker thread procedure."
   (parameterize (((@@ (fibers internal) current-fiber) #f))
     (let ((channel (make-channel)))
       (call-with-new-thread
        (lambda ()
-         (parameterize ((%critical-section-args args))
+         (parameterize ((%worker-thread-args args))
            (let loop ()
              (match (get-message channel)
                (((? channel? reply) . (? procedure? proc))
@@ -118,21 +114,21 @@ dedicated thread."
              (loop)))))
       channel)))
 
-(define (call-with-critical-section channel proc)
-  "Send PROC to the critical section through CHANNEL.  Return the result of
-PROC.  If already in the critical section, call PROC immediately."
-  (let ((args (%critical-section-args)))
+(define (call-with-worker-thread channel proc)
+  "Send PROC to the worker thread through CHANNEL.  Return the result of PROC.
+If already in the worker thread, call PROC immediately."
+  (let ((args (%worker-thread-args)))
     (if args
         (apply proc args)
         (let ((reply (make-channel)))
           (put-message channel (cons reply proc))
           (get-message reply)))))
 
-(define-syntax-rule (with-critical-section channel (vars ...) exp ...)
-  "Evaluate EXP... in the critical section corresponding to CHANNEL.
-VARS... are bound to the arguments of the critical section."
-  (call-with-critical-section channel
-                              (lambda (vars ...) exp ...)))
+(define-syntax-rule (with-worker-thread channel (vars ...) exp ...)
+  "Evaluate EXP... in the worker thread corresponding to CHANNEL.
+VARS... are bound to the arguments of the worker thread."
+  (call-with-worker-thread channel
+                           (lambda (vars ...) exp ...)))
 
 (define (%non-blocking thunk)
   (parameterize (((@@ (fibers internal) current-fiber) #f))
-- 
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