From 594dfafdf4182a029d797b260518f41d40328d23 Mon Sep 17 00:00:00 2001
From: Ryan Culpepper <ryanc@racket-lang.org>
Date: Sun, 14 Feb 2021 01:27:40 +0100
Subject: [PATCH] db: factor out ffi-common mixin

---
 .../db/private/generic/ffi-common.rkt         | 115 ++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 racket/collects/db/private/generic/ffi-common.rkt

diff --git a/racket/collects/db/private/generic/ffi-common.rkt b/racket/collects/db/private/generic/ffi-common.rkt
new file mode 100644
index 0000000000..bf38c7bae3
--- /dev/null
+++ b/racket/collects/db/private/generic/ffi-common.rkt
@@ -0,0 +1,115 @@
+#lang racket/base
+(require racket/class
+         ffi/unsafe/atomic
+         ffi/unsafe/custodian
+         ffi/unsafe/os-thread
+         ffi/unsafe/os-async-channel
+         "interfaces.rkt")
+(provide (protect-out
+          ffi-connection-mixin))
+
+;; Convention: methods names starting with "-" usually indicate methods that
+;; must be called in atomic mode.
+
+(define (ffi-connection-mixin %)
+  (class %
+    (inherit call-with-lock)
+    (super-new)
+
+    ;; -get-db : -> DB/#f
+    (abstract -get-db)
+
+    ;; -get-do-disconnect : -> (-> (-> Void))
+    ;; Partially disconnect (ie, mark as disconnected) and return a closure that
+    ;; finishes disconnecting and returns a closure to report disconnection errors.
+    ;; The first closure result may be called in an OS thread.
+    ;; The second closure result is always called in a Racket thread (but maybe atomic).
+    (abstract -get-do-disconnect)
+
+    ;; ----------------------------------------
+    ;; Disconnect
+
+    (define/override (disconnect* _politely?)
+      (super disconnect* _politely?)
+      (real-disconnect))
+
+    (define/public (real-disconnect)
+      (call-as-atomic
+       (lambda ()
+         (when (-get-db)
+           ;; Partially disconnect
+           (define do-disconnect (-get-do-disconnect))
+           ;; Finish disconnecting
+           (cond [os-req-chan
+                  ;; OS thread might be using db, stmts
+                  (define resp-chan (make-os-async-channel))
+                  (define (shutdown _db)
+                    (define done (do-disconnect))
+                    (when resp-chan (os-async-channel-put resp-chan done)))
+                  (log-db-debug "disconnect delayed to OS thread")
+                  (os-async-channel-put os-req-chan (cons shutdown #f))
+                  (when resp-chan
+                    (parameterize ((current-custodian (make-custodian-at-root)))
+                      (thread
+                       (lambda ()
+                         (define done (sync resp-chan))
+                         (log-db-debug "finished delayed disconnect")
+                         (done)))))
+                  (void)]
+                 [else ((do-disconnect))])))))
+
+    ;; ----------------------------------------
+    ;; OS Thread Support
+
+    (define use-os-thread? #f)
+    (define os-req-chan #f)  ;; #f or OS-Async-Channel
+    (define os-resp-chan #f) ;; #f or OS-Async-Channel
+
+    (define/public (get-use-os-thread?) use-os-thread?)
+
+    (define/public (use-os-thread use?)
+      (when use?
+        (unless (os-thread-enabled?)
+          (raise (exn:fail:unsupported "use-os-thread: not supported"
+                                       (current-continuation-marks)))))
+      (call-with-lock 'use-os-thread
+        (lambda ()
+          (set! use-os-thread? (and use? #t))
+          (when use?
+            (call-as-atomic
+             (lambda ()
+               (unless os-req-chan
+                 (define db (-get-db))
+                 (define req-chan (make-os-async-channel))
+                 (define resp-chan (make-os-async-channel))
+                 (call-in-os-thread
+                  (lambda ()
+                    (let loop ()
+                      (define msg (os-async-channel-get req-chan))
+                      (define proc (car msg))
+                      (define loop? (cdr msg))
+                      (os-async-channel-put resp-chan (proc db))
+                      (when loop? (loop)))))
+                 (set! os-req-chan req-chan)
+                 (set! os-resp-chan resp-chan))))))))
+
+    ;; sync-call-in-os-thread : (DB/#f -> X) -> X
+    ;; Calls proc either normally or in an OS thread. If in OS thread, proc is
+    ;; passed the saved DB value (in case of partial disconnects); if called
+    ;; normally, proc is passed #f.
+    (define/public (sync-call-in-os-thread proc)
+      (start-atomic)
+      (cond [(-get-db)
+             (when os-req-chan
+               (os-async-channel-put os-req-chan (cons proc #t)))
+             (end-atomic)]
+            [else
+             (end-atomic)
+             (error)])
+      (sync os-resp-chan))
+
+    ;; sync-call : (DB/#f -> X) -> X
+    (define/public (sync-call proc)
+      (cond [use-os-thread? (sync-call-in-os-thread proc)]
+            [else (proc #f)]))
+    ))