From 40676067383d8fef9cc1690154011708c7e8e256 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <mhw@netris.org>
Date: Sun, 17 Nov 2013 02:54:31 -0500
Subject: [PATCH 6/6] Make (ice-9 popen) thread-safe.

* module/ice-9/popen.scm: Import (ice-9 threads).
  (port/pid-table): Mark as deprecated in comment.
  (port/pid-table-mutex): New variable.
  (open-pipe*): Stash the pid in the port's alist.  Lock
  'port/pid-table-mutex' while mutating 'port/pid-table'.
  (fetch-pid): Fetch the pid from the port's alist.  Don't touch
  'port/pid-table'.
  (close-process-quietly): Don't add the port to 'port/pid-table-mutex',
  since it was never removed.
  (close-pipe): Improve error message.
  (reap-pipes): Check to see if the port is already closed.
---
 module/ice-9/popen.scm |   27 +++++++++++++++++----------
 1 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/module/ice-9/popen.scm b/module/ice-9/popen.scm
index f8668cd..0e896d7 100644
--- a/module/ice-9/popen.scm
+++ b/module/ice-9/popen.scm
@@ -18,6 +18,7 @@
 ;;;; 
 
 (define-module (ice-9 popen)
+  :use-module (ice-9 threads)
   :export (port/pid-table open-pipe* open-pipe close-pipe open-input-pipe
 	   open-output-pipe open-input-output-pipe))
 
@@ -40,7 +41,10 @@
 (define pipe-guardian (make-guardian))
 
 ;; a weak hash-table to store the process ids.
+;; XXX use of this table is deprecated.  It is no longer used, and is
+;; populated only for backward compatibility (since it is exported).
 (define port/pid-table (make-weak-key-hash-table 31))
+(define port/pid-table-mutex (make-mutex))
 
 (define (open-pipe* mode command . args)
   "Executes the program @var{command} with optional arguments
@@ -57,8 +61,13 @@ port to the process is created: it should be the value of
                       read-port
                       write-port
                       (%make-void-port mode))))
+        (%set-port-alist! port (acons 'popen-pid pid (%port-alist port)))
         (pipe-guardian port)
-        (hashq-set! port/pid-table port pid)
+
+        ;; XXX populate port/pid-table for backward compatibility.
+        (with-mutex port/pid-table-mutex
+          (hashq-set! port/pid-table port pid))
+
         port))))
 
 (define (open-pipe command mode)
@@ -70,9 +79,7 @@ port to the process is created: it should be the value of
   (open-pipe* mode "/bin/sh" "-c" command))
 
 (define (fetch-pid port)
-  (let ((pid (hashq-ref port/pid-table port)))
-    (hashq-remove! port/pid-table port)
-    pid))
+  (assq-ref (%port-alist port) 'popen-pid))
 
 (define (close-process port pid)
   (close-port port)
@@ -92,8 +99,7 @@ port to the process is created: it should be the value of
 	   (let ((pid/status (waitpid pid WNOHANG)))
              (when (zero? (car pid/status))
                ;; not ready for collection
-               (pipe-guardian port)
-               (hashq-set! port/pid-table port pid))))
+               (pipe-guardian port))))
 	 (lambda args #f)))
 
 (define (close-pipe p)
@@ -101,16 +107,17 @@ port to the process is created: it should be the value of
 to terminate and returns its status value, @xref{Processes, waitpid}, for
 information on how to interpret this value."
   (let ((pid (fetch-pid p)))
-    (unless pid (error "close-pipe: pipe not in table"))
+    (unless pid (error "close-pipe: pipe not created by (ice-9 popen)"))
     (close-process p pid)))
 
 (define (reap-pipes)
   (let loop ()
     (let ((p (pipe-guardian)))
       (when p
-        ;; maybe removed already by close-pipe.
-        (let ((pid (fetch-pid p)))
-          (when pid (close-process-quietly p pid)))
+        ;; maybe closed already.
+        (unless (port-closed? p)
+          (let ((pid (fetch-pid p)))
+            (when pid (close-process-quietly p pid))))
         (loop)))))
 
 (add-hook! after-gc-hook reap-pipes)
-- 
1.7.5.4