Re: [Qemu-devel] [PATCH] util/qemu-thread-posix.c: Replace OS ifdefs with CONFIG_HAVE_SEM_TIMEDWAIT

[Michael Tokarev]

05.09.2017 15:19, Peter Maydell wrote:
> In qemu-thread-posix.c we have two implementations of the
> various qemu_sem_* functions, one of which uses native POSIX
> sem_* and the other of which emulates them with pthread conditions.
> This is necessary because not all our host OSes support
> sem_timedwait().
..

Applied to -trivial, thanks!

/mjt

Re: [Qemu-devel] [PATCH] util/qemu-thread-posix.c: Replace OS ifdefs with CONFIG_HAVE_SEM_TIMEDWAIT

[Eric Blake]

On 09/05/2017 07:19 AM, Peter Maydell wrote:
> In qemu-thread-posix.c we have two implementations of the
> various qemu_sem_* functions, one of which uses native POSIX
> sem_* and the other of which emulates them with pthread conditions.
> This is necessary because not all our host OSes support
> sem_timedwait().
> 
> Instead of a hard-coded list of OSes which don't implement
> sem_timedwait(), which gets out of date, make configure
> test for the presence of the function and set a new
> CONFIG_HAVE_SEM_TIMEDWAIT appropriately.
> 
> In particular, newer NetBSDs have sem_timedwait(), so this
> commit will switch them over to using it. OSX still does
> not have an implementation.
> 
> Signed-off-by: Peter Maydell 
> ---
> It would be nice to gradually reduce the number of places
> we do per-OS ifdeffery in favour of checking for the specific
> feature we care about in each case...

Yes, that's always been autoconf's philosophy: feature tests trump
platform tests every time, because platforms can add features over time,
and because an ifdef on a single feature test is easier to read than a
list of platform names.

> Tested on Linux, NetBSD, OSX.
> 

Reviewed-by: Eric Blake 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.   +1-919-301-3266
Virtualization:  qemu.org | libvirt.org



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[Qemu-devel] [PATCH] util/qemu-thread-posix.c: Replace OS ifdefs with CONFIG_HAVE_SEM_TIMEDWAIT

[Peter Maydell]

In qemu-thread-posix.c we have two implementations of the
various qemu_sem_* functions, one of which uses native POSIX
sem_* and the other of which emulates them with pthread conditions.
This is necessary because not all our host OSes support
sem_timedwait().

Instead of a hard-coded list of OSes which don't implement
sem_timedwait(), which gets out of date, make configure
test for the presence of the function and set a new
CONFIG_HAVE_SEM_TIMEDWAIT appropriately.

In particular, newer NetBSDs have sem_timedwait(), so this
commit will switch them over to using it. OSX still does
not have an implementation.

Signed-off-by: Peter Maydell 
---
It would be nice to gradually reduce the number of places
we do per-OS ifdeffery in favour of checking for the specific
feature we care about in each case...
Tested on Linux, NetBSD, OSX.

 configure   | 15 +++
 include/qemu/thread-posix.h |  2 +-
 util/qemu-thread-posix.c| 10 +-
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/configure b/configure
index fb7e34a..aa8d4d9 100755
--- a/configure
+++ b/configure
@@ -4448,6 +4448,18 @@ if compile_prog "" "" ; then
 fi
 
 ##
+# check if we have sem_timedwait
+
+sem_timedwait=no
+cat > $TMPC << EOF
+#include 
+int main(void) { return sem_timedwait(0, 0); }
+EOF
+if compile_prog "" "" ; then
+sem_timedwait=yes
+fi
+
+##
 # check if trace backend exists
 
 $python "$source_path/scripts/tracetool.py" "--backends=$trace_backends" 
--check-backends  > /dev/null 2> /dev/null
@@ -5680,6 +5692,9 @@ fi
 if test "$inotify1" = "yes" ; then
   echo "CONFIG_INOTIFY1=y" >> $config_host_mak
 fi
+if test "$sem_timedwait" = "yes" ; then
+  echo "CONFIG_SEM_TIMEDWAIT=y" >> $config_host_mak
+fi
 if test "$byteswap_h" = "yes" ; then
   echo "CONFIG_BYTESWAP_H=y" >> $config_host_mak
 fi
diff --git a/include/qemu/thread-posix.h b/include/qemu/thread-posix.h
index e5e3a0f..f4296d3 100644
--- a/include/qemu/thread-posix.h
+++ b/include/qemu/thread-posix.h
@@ -21,7 +21,7 @@ struct QemuCond {
 };
 
 struct QemuSemaphore {
-#if defined(__APPLE__) || defined(__NetBSD__)
+#ifndef CONFIG_SEM_TIMEDWAIT
 pthread_mutex_t lock;
 pthread_cond_t cond;
 unsigned int count;
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index 4e95d27..7306475 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -168,7 +168,7 @@ void qemu_sem_init(QemuSemaphore *sem, int init)
 {
 int rc;
 
-#if defined(__APPLE__) || defined(__NetBSD__)
+#ifndef CONFIG_SEM_TIMEDWAIT
 rc = pthread_mutex_init(>lock, NULL);
 if (rc != 0) {
 error_exit(rc, __func__);
@@ -196,7 +196,7 @@ void qemu_sem_destroy(QemuSemaphore *sem)
 
 assert(sem->initialized);
 sem->initialized = false;
-#if defined(__APPLE__) || defined(__NetBSD__)
+#ifndef CONFIG_SEM_TIMEDWAIT
 rc = pthread_cond_destroy(>cond);
 if (rc < 0) {
 error_exit(rc, __func__);
@@ -218,7 +218,7 @@ void qemu_sem_post(QemuSemaphore *sem)
 int rc;
 
 assert(sem->initialized);
-#if defined(__APPLE__) || defined(__NetBSD__)
+#ifndef CONFIG_SEM_TIMEDWAIT
 pthread_mutex_lock(>lock);
 if (sem->count == UINT_MAX) {
 rc = EINVAL;
@@ -256,7 +256,7 @@ int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
 struct timespec ts;
 
 assert(sem->initialized);
-#if defined(__APPLE__) || defined(__NetBSD__)
+#ifndef CONFIG_SEM_TIMEDWAIT
 rc = 0;
 compute_abs_deadline(, ms);
 pthread_mutex_lock(>lock);
@@ -304,7 +304,7 @@ void qemu_sem_wait(QemuSemaphore *sem)
 int rc;
 
 assert(sem->initialized);
-#if defined(__APPLE__) || defined(__NetBSD__)
+#ifndef CONFIG_SEM_TIMEDWAIT
 pthread_mutex_lock(>lock);
 while (sem->count == 0) {
 rc = pthread_cond_wait(>cond, >lock);
-- 
2.7.4