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[PATCH] Make guardians and (ice-9 popen) thread-safe
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From: |
Mark H Weaver |
|
Subject: |
[PATCH] Make guardians and (ice-9 popen) thread-safe |
|
Date: |
Mon, 18 Nov 2013 01:12:54 -0500 |
Hello all,
Here's a set of patches for stable-2.0 that make (ice-9 popen) and
guardians thread-safe. These patches fix <http://bugs.gnu.org/15683>.
(please disregard the preliminary patches I posted in that bug report).
These patches also lay the groundwork for conveniently blocking asyncs
while mutexes are held, to prevent the deadlocks that can arise when
asyncs are run while a mutex is held, and one of the asyncs runs code
that tries to lock the same mutex, as discussed here:
http://lists.gnu.org/archive/html/guile-devel/2013-08/msg00025.html
http://lists.gnu.org/archive/html/guile-devel/2013-08/msg00030.html
In this patch set, I only block asyncs in two places: when the guardian
mutex is held, and when the 'overrides_lock' is held in procprop.scm,
which has caused deadlocks for me in practice. However, in the future
I'd like to make a more comprehensive effort to find other places where
this should be done.
Comments and suggestions welcome.
Mark
>From e4b90f498c3141ba203a6359a8a0cfe790324203 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Sun, 17 Nov 2013 04:00:29 -0500
Subject: [PATCH 1/6] Add mutex locking functions that also block asyncs.
* libguile/async.h (scm_i_pthread_mutex_lock_with_asyncs,
scm_i_pthread_mutex_unlock_with_asyncs): New macros.
* libguile/threads.c (do_unlock_with_asyncs): New static helper.
(scm_i_dynwind_pthread_mutex_lock_with_asyncs): New function.
* libguile/threads.h (scm_i_dynwind_pthread_mutex_lock_with_asyncs):
Add prototype.
---
libguile/async.h | 16 ++++++++++++++++
libguile/threads.c | 16 ++++++++++++++++
libguile/threads.h | 1 +
3 files changed, 33 insertions(+), 0 deletions(-)
diff --git a/libguile/async.h b/libguile/async.h
index ceb2b96..a909c0d 100644
--- a/libguile/async.h
+++ b/libguile/async.h
@@ -78,6 +78,22 @@ SCM_API void scm_critical_section_end (void);
scm_async_click (); \
} while (0)
+# define scm_i_pthread_mutex_lock_with_asyncs(m) \
+ do \
+ { \
+ SCM_I_CURRENT_THREAD->block_asyncs++; \
+ scm_i_pthread_mutex_lock (m); \
+ } \
+ while (0)
+
+# define scm_i_pthread_mutex_unlock_with_asyncs(m) \
+ do \
+ { \
+ scm_i_pthread_mutex_unlock (m); \
+ SCM_I_CURRENT_THREAD->block_asyncs--; \
+ } \
+ while (0)
+
#else /* !BUILDING_LIBGUILE */
# define SCM_CRITICAL_SECTION_START scm_critical_section_start ()
diff --git a/libguile/threads.c b/libguile/threads.c
index 8cbe1e2..6aeaeb9 100644
--- a/libguile/threads.c
+++ b/libguile/threads.c
@@ -2010,6 +2010,22 @@ scm_pthread_cond_timedwait (scm_i_pthread_cond_t *cond,
#endif
+static void
+do_unlock_with_asyncs (void *data)
+{
+ scm_i_pthread_mutex_unlock ((scm_i_pthread_mutex_t *)data);
+ SCM_I_CURRENT_THREAD->block_asyncs--;
+}
+
+void
+scm_i_dynwind_pthread_mutex_lock_with_asyncs (scm_i_pthread_mutex_t *mutex)
+{
+ SCM_I_CURRENT_THREAD->block_asyncs++;
+ scm_i_scm_pthread_mutex_lock (mutex);
+ scm_dynwind_unwind_handler (do_unlock_with_asyncs, mutex,
+ SCM_F_WIND_EXPLICITLY);
+}
+
unsigned long
scm_std_usleep (unsigned long usecs)
{
diff --git a/libguile/threads.h b/libguile/threads.h
index 901c37b..5a2afa2 100644
--- a/libguile/threads.h
+++ b/libguile/threads.h
@@ -143,6 +143,7 @@ SCM_INTERNAL void scm_init_threads (void);
SCM_INTERNAL void scm_init_thread_procs (void);
SCM_INTERNAL void scm_init_threads_default_dynamic_state (void);
+SCM_INTERNAL void scm_i_dynwind_pthread_mutex_lock_with_asyncs
(scm_i_pthread_mutex_t *mutex);
#define SCM_THREAD_SWITCHING_CODE \
do { } while (0)
--
1.7.5.4
>From 13fcd175bc31b5df400dd518836bdce32f32206a Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Sun, 17 Nov 2013 03:19:32 -0500
Subject: [PATCH 2/6] Block system asyncs while 'overrides_lock' is held.
* libguile/procprop.c (scm_set_procedure_property_x): Block system
asyncs while overrides_lock is held. Use dynwind block in case
an exception is thrown.
---
libguile/procprop.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/libguile/procprop.c b/libguile/procprop.c
index 36228d3..dae3ea7 100644
--- a/libguile/procprop.c
+++ b/libguile/procprop.c
@@ -229,7 +229,8 @@ SCM_DEFINE (scm_set_procedure_property_x,
"set-procedure-property!", 3, 0, 0,
SCM_MISC_ERROR ("arity is a deprecated read-only property", SCM_EOL);
#endif
- scm_i_pthread_mutex_lock (&overrides_lock);
+ scm_dynwind_begin (0);
+ scm_i_dynwind_pthread_mutex_lock_with_asyncs (&overrides_lock);
props = scm_hashq_ref (overrides, proc, SCM_BOOL_F);
if (scm_is_false (props))
{
@@ -239,7 +240,7 @@ SCM_DEFINE (scm_set_procedure_property_x,
"set-procedure-property!", 3, 0, 0,
props = SCM_EOL;
}
scm_hashq_set_x (overrides, proc, scm_assq_set_x (props, key, val));
- scm_i_pthread_mutex_unlock (&overrides_lock);
+ scm_dynwind_end ();
return SCM_UNSPECIFIED;
}
--
1.7.5.4
>From 73d674d1983e7777f22d43335a1834bf26606494 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Sun, 17 Nov 2013 03:35:09 -0500
Subject: [PATCH 3/6] Make guardians thread-safe.
* libguile/guardians.c (t_guardian): Add mutex.
(finalize_guarded, scm_i_guard, scm_i_get_one_zombie): Lock mutex and
block system asyncs during critical sections.
(scm_make_guardian): Initialize mutex.
---
libguile/guardians.c | 18 ++++++++++++++++--
1 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/libguile/guardians.c b/libguile/guardians.c
index 6ba8c0b..e59e1bb 100644
--- a/libguile/guardians.c
+++ b/libguile/guardians.c
@@ -40,7 +40,6 @@
* monsters we had...
*
* Rewritten for the Boehm-Demers-Weiser GC by Ludovic Courtès.
- * FIXME: This is currently not thread-safe.
*/
/* Uncomment the following line to debug guardian finalization. */
@@ -72,6 +71,7 @@ static scm_t_bits tc16_guardian;
typedef struct t_guardian
{
+ scm_i_pthread_mutex_t mutex;
unsigned long live;
SCM zombies;
struct t_guardian *next;
@@ -144,6 +144,9 @@ finalize_guarded (void *ptr, void *finalizer_data)
}
g = GUARDIAN_DATA (SCM_CAR (guardian_list));
+
+ scm_i_pthread_mutex_lock_with_asyncs (&g->mutex);
+
if (g->live == 0)
abort ();
@@ -157,7 +160,8 @@ finalize_guarded (void *ptr, void *finalizer_data)
g->zombies = zombies;
g->live--;
- g->zombies = zombies;
+
+ scm_i_pthread_mutex_unlock_with_asyncs (&g->mutex);
}
if (scm_is_true (proxied_finalizer))
@@ -208,6 +212,8 @@ scm_i_guard (SCM guardian, SCM obj)
void *prev_data;
SCM guardians_for_obj, finalizer_data;
+ scm_i_pthread_mutex_lock_with_asyncs (&g->mutex);
+
g->live++;
/* Note: GUARDIANS_FOR_OBJ is a weak list so that a guardian can be
@@ -249,6 +255,8 @@ scm_i_guard (SCM guardian, SCM obj)
PTR2SCM (prev_data));
SCM_SETCAR (finalizer_data, proxied_finalizer);
}
+
+ scm_i_pthread_mutex_unlock_with_asyncs (&g->mutex);
}
}
@@ -258,6 +266,8 @@ scm_i_get_one_zombie (SCM guardian)
t_guardian *g = GUARDIAN_DATA (guardian);
SCM res = SCM_BOOL_F;
+ scm_i_pthread_mutex_lock_with_asyncs (&g->mutex);
+
if (!scm_is_null (g->zombies))
{
/* Note: We return zombies in reverse order. */
@@ -265,6 +275,8 @@ scm_i_get_one_zombie (SCM guardian)
g->zombies = SCM_CDR (g->zombies);
}
+ scm_i_pthread_mutex_unlock_with_asyncs (&g->mutex);
+
return res;
}
@@ -335,6 +347,8 @@ SCM_DEFINE (scm_make_guardian, "make-guardian", 0, 0, 0,
t_guardian *g = scm_gc_malloc (sizeof (t_guardian), "guardian");
SCM z;
+ scm_i_pthread_mutex_init (&g->mutex, NULL);
+
/* A tconc starts out with one tail pair. */
g->live = 0;
g->zombies = SCM_EOL;
--
1.7.5.4
>From f89b0a7adf9260fee39dd82e756edfabcdf1a668 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Sun, 17 Nov 2013 01:11:57 -0500
Subject: [PATCH 4/6] Make port alists accessible from Scheme.
* libguile/ports.c (scm_i_port_alist, scm_i_set_port_alist_x): Make
these available from Scheme, as '%port-alist' and '%set-port-alist!'.
Validate port argument.
* libguile/ports.h (scm_i_set_port_alist_x): Change return type from
'void' to 'SCM'.
---
libguile/ports.c | 17 +++++++++++++----
libguile/ports.h | 2 +-
2 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/libguile/ports.c b/libguile/ports.c
index 6f219d6..030090c 100644
--- a/libguile/ports.c
+++ b/libguile/ports.c
@@ -254,17 +254,26 @@ scm_i_clear_pending_eof (SCM port)
SCM_PORT_GET_INTERNAL (port)->pending_eof = 0;
}
-SCM
-scm_i_port_alist (SCM port)
+SCM_DEFINE (scm_i_port_alist, "%port-alist", 1, 0, 0,
+ (SCM port),
+ "Return the alist associated with @var{port}.")
+#define FUNC_NAME s_scm_i_port_alist
{
+ SCM_VALIDATE_OPPORT (1, port);
return SCM_PORT_GET_INTERNAL (port)->alist;
}
+#undef FUNC_NAME
-void
-scm_i_set_port_alist_x (SCM port, SCM alist)
+SCM_DEFINE (scm_i_set_port_alist_x, "%set-port-alist!", 2, 0, 0,
+ (SCM port, SCM alist),
+ "Set the alist associated with @var{port} to @var{alist}.")
+#define FUNC_NAME s_scm_i_set_port_alist_x
{
+ SCM_VALIDATE_OPPORT (1, port);
SCM_PORT_GET_INTERNAL (port)->alist = alist;
+ return SCM_UNSPECIFIED;
}
+#undef FUNC_NAME
diff --git a/libguile/ports.h b/libguile/ports.h
index 39317f8..c8d08df 100644
--- a/libguile/ports.h
+++ b/libguile/ports.h
@@ -318,7 +318,7 @@ SCM_API SCM scm_set_port_column_x (SCM port, SCM line);
SCM_API SCM scm_port_filename (SCM port);
SCM_API SCM scm_set_port_filename_x (SCM port, SCM filename);
SCM_INTERNAL SCM scm_i_port_alist (SCM port);
-SCM_INTERNAL void scm_i_set_port_alist_x (SCM port, SCM alist);
+SCM_INTERNAL SCM scm_i_set_port_alist_x (SCM port, SCM alist);
SCM_INTERNAL const char *scm_i_default_port_encoding (void);
SCM_INTERNAL void scm_i_set_default_port_encoding (const char *);
SCM_INTERNAL void scm_i_set_port_encoding_x (SCM port, const char *str);
--
1.7.5.4
>From b53342d28a0ec0844373c1469d5f56d4cb6d98fc Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Sun, 17 Nov 2013 02:46:08 -0500
Subject: [PATCH 5/6] Stylistic improvements for (ice-9 popen).
* module/ice-9/popen.scm (close-process, close-process-quietly): Accept
'port' and 'pid' as separate arguments. Improve style.
(close-pipe, read-pipes): Improve style.
---
module/ice-9/popen.scm | 45 +++++++++++++++++++++------------------------
1 files changed, 21 insertions(+), 24 deletions(-)
diff --git a/module/ice-9/popen.scm b/module/ice-9/popen.scm
index 7d0549e..f8668cd 100644
--- a/module/ice-9/popen.scm
+++ b/module/ice-9/popen.scm
@@ -74,27 +74,26 @@ port to the process is created: it should be the value of
(hashq-remove! port/pid-table port)
pid))
-(define (close-process port/pid)
- (close-port (car port/pid))
- (cdr (waitpid (cdr port/pid))))
+(define (close-process port pid)
+ (close-port port)
+ (cdr (waitpid pid)))
;; for the background cleanup handler: just clean up without reporting
;; errors. also avoids blocking the process: if the child isn't ready
;; to be collected, puts it back into the guardian's live list so it
;; can be tried again the next time the cleanup runs.
-(define (close-process-quietly port/pid)
+(define (close-process-quietly port pid)
(catch 'system-error
(lambda ()
- (close-port (car port/pid)))
+ (close-port port))
(lambda args #f))
(catch 'system-error
(lambda ()
- (let ((pid/status (waitpid (cdr port/pid) WNOHANG)))
- (cond ((= (car pid/status) 0)
- ;; not ready for collection
- (pipe-guardian (car port/pid))
- (hashq-set! port/pid-table
- (car port/pid) (cdr port/pid))))))
+ (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))))
(lambda args #f)))
(define (close-pipe p)
@@ -102,19 +101,17 @@ 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)))
- (if (not pid)
- (error "close-pipe: pipe not in table"))
- (close-process (cons p pid))))
-
-(define reap-pipes
- (lambda ()
- (let loop ((p (pipe-guardian)))
- (cond (p
- ;; maybe removed already by close-pipe.
- (let ((pid (fetch-pid p)))
- (if pid
- (close-process-quietly (cons p pid))))
- (loop (pipe-guardian)))))))
+ (unless pid (error "close-pipe: pipe not in table"))
+ (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)))
+ (loop)))))
(add-hook! after-gc-hook reap-pipes)
--
1.7.5.4
>From 3c3e66b85d294fc5ded6f6660a0efe00ed6519b9 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
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*): Store the pid in the port's alist. Guard the alist
entry instead of the port. Lock 'port/pid-table-mutex' while mutating
'port/pid-table'.
(fetch-pid): Removed.
(fetch-alist-entry): New procedure.
(close-process-quietly): Removed.
(close-pipe): Use 'fetch-alist-entry' instead of 'fetch-pid'. Clear
the cdr of the alist entry. Improve error messages.
(reap-pipes): Adapt to the fact that the alist entries are now guarded
instead of the ports. Incorporate the 'waitpid' code that was
previously in 'close-process-quietly', but let the port finalizer
close the port. Clear the cdr of the alist entry.
---
module/ice-9/popen.scm | 80 +++++++++++++++++++++++++++--------------------
1 files changed, 46 insertions(+), 34 deletions(-)
diff --git a/module/ice-9/popen.scm b/module/ice-9/popen.scm
index f8668cd..2a9f566 100644
--- a/module/ice-9/popen.scm
+++ b/module/ice-9/popen.scm
@@ -1,6 +1,7 @@
;; popen emulation, for non-stdio based ports.
-;;;; Copyright (C) 1998, 1999, 2000, 2001, 2003, 2006, 2010, 2011, 2012, 2013
Free Software Foundation, Inc.
+;;;; Copyright (C) 1998, 1999, 2000, 2001, 2003, 2006, 2010, 2011, 2012,
+;;;; 2013 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
@@ -18,6 +19,7 @@
;;;;
(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 +42,10 @@
(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 here, and
+;; is populated for backward compatibility only (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
@@ -56,9 +61,19 @@ port to the process is created: it should be the value of
(make-rw-port read-port write-port))
read-port
write-port
- (%make-void-port mode))))
- (pipe-guardian port)
- (hashq-set! port/pid-table port pid)
+ (%make-void-port mode)))
+ (alist-entry (cons 'popen-pid pid)))
+
+ ;; Guard the alist-entry instead of the port, so that we can
+ ;; still call 'waitpid' even if 'close-port' is called (which
+ ;; clears the port entry).
+ (pipe-guardian alist-entry)
+ (%set-port-alist! port (cons alist-entry (%port-alist port)))
+
+ ;; 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)
@@ -69,48 +84,45 @@ port to the process is created: it should be the value of
@code{OPEN_READ}, @code{OPEN_WRITE} or @code{OPEN_BOTH}."
(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))
+(define (fetch-alist-entry port)
+ (assq 'popen-pid (%port-alist port)))
(define (close-process port pid)
(close-port port)
(cdr (waitpid pid)))
-;; for the background cleanup handler: just clean up without reporting
-;; errors. also avoids blocking the process: if the child isn't ready
-;; to be collected, puts it back into the guardian's live list so it
-;; can be tried again the next time the cleanup runs.
-(define (close-process-quietly port pid)
- (catch 'system-error
- (lambda ()
- (close-port port))
- (lambda args #f))
- (catch 'system-error
- (lambda ()
- (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))))
- (lambda args #f)))
-
(define (close-pipe p)
"Closes the pipe created by @code{open-pipe}, then waits for the process
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"))
- (close-process p pid)))
+ (let ((alist-entry (fetch-alist-entry p)))
+ (unless alist-entry
+ (error "close-pipe: port not created by (ice-9 popen)"))
+ (let ((pid (cdr alist-entry)))
+ ;; set the cdr to #f to avoid repeated calls to 'waitpid'.
+ (unless pid
+ (error "close-pipe: pid has already been cleared"))
+ (set-cdr! alist-entry #f)
+ (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)))
+ (let ((alist-entry (pipe-guardian)))
+ (when alist-entry
+ (let ((pid (cdr alist-entry)))
+ ;; maybe 'close-pipe' was already called.
+ (when pid
+ ;; clean up without reporting errors. also avoids blocking
+ ;; the process: if the child isn't ready to be collected,
+ ;; puts it back into the guardian's live list so it can be
+ ;; tried again the next time the cleanup runs.
+ (catch 'system-error
+ (lambda ()
+ (let ((pid/status (waitpid pid WNOHANG)))
+ (if (zero? (car pid/status))
+ (pipe-guardian alist-entry) ; not ready for collection
+ (set-cdr! alist-entry #f)))) ; avoid calling waitpid
again
+ (lambda args #f))))
(loop)))))
(add-hook! after-gc-hook reap-pipes)
--
1.7.5.4
- [PATCH] Make guardians and (ice-9 popen) thread-safe,
Mark H Weaver <=