Patchwork [v3,01/10] Introduce qemu_cond_timedwait for POSIX

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Submitter Jan Kiszka
Date April 5, 2012, 10:59 a.m.
Message ID <6e10c02cbb87fe30703de848455593df41ec7f4b.1333623555.git.jan.kiszka@siemens.com>
Download mbox | patch
Permalink /patch/151181/
State New
Headers show

Comments

Jan Kiszka - April 5, 2012, 10:59 a.m.
First user will be POSIX compat aio. Windows use cases aren't in sight,
so this remains a POSIX-only service for now.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 qemu-thread-posix.c |   23 +++++++++++++++++++++++
 qemu-thread-posix.h |    5 +++++
 2 files changed, 28 insertions(+), 0 deletions(-)
malc - April 5, 2012, 1 p.m.
On Thu, 5 Apr 2012, Jan Kiszka wrote:

> On 2012-04-05 14:56, Paolo Bonzini wrote:
> > Il 05/04/2012 14:53, malc ha scritto:
> >> On Thu, 5 Apr 2012, Paolo Bonzini wrote:
> >>
> >>> Il 05/04/2012 14:30, malc ha scritto:
> >>>>>> Would save that "* 1000". I just wondered why we do not use it elsewhere
> >>>>>> in QEMU and was reluctant to risk some BSD breakage.
> >>>>>>
> >>>> It's probably worth mentioning that using anything other than 
> >>>> clock_gettime and CLOCK_MONOTONING (as well as setting proper pthread
> >>>> clock attr on the condition variable) is prone to the surprises (such
> >>>> as NTP corrections and daylight saving changes).
> >>>
> >>> I was about to suggest the same, but how widespread is support for
> >>> pthread_condattr_setclock?
> >>
> >> If it's not all is lost anyway.
> > 
> > Only once every year. :)
> 
> ...and not for the current user of this service which do not care that
> much about the timeout and a potential delay or early shot.
> 

An hour of potential delay mind you.
Jan Kiszka - April 5, 2012, 1:24 p.m.
On 2012-04-05 15:20, malc wrote:
> On Thu, 5 Apr 2012, Jan Kiszka wrote:
> 
>> On 2012-04-05 15:00, malc wrote:
>>> On Thu, 5 Apr 2012, Jan Kiszka wrote:
>>>
>>>> On 2012-04-05 14:56, Paolo Bonzini wrote:
>>>>> Il 05/04/2012 14:53, malc ha scritto:
>>>>>> On Thu, 5 Apr 2012, Paolo Bonzini wrote:
>>>>>>
>>>>>>> Il 05/04/2012 14:30, malc ha scritto:
>>>>>>>>>> Would save that "* 1000". I just wondered why we do not use it elsewhere
>>>>>>>>>> in QEMU and was reluctant to risk some BSD breakage.
>>>>>>>>>>
>>>>>>>> It's probably worth mentioning that using anything other than 
>>>>>>>> clock_gettime and CLOCK_MONOTONING (as well as setting proper pthread
>>>>>>>> clock attr on the condition variable) is prone to the surprises (such
>>>>>>>> as NTP corrections and daylight saving changes).
>>>>>>>
>>>>>>> I was about to suggest the same, but how widespread is support for
>>>>>>> pthread_condattr_setclock?
>>>>>>
>>>>>> If it's not all is lost anyway.
>>>>>
>>>>> Only once every year. :)
>>>>
>>>> ...and not for the current user of this service which do not care that
>>>> much about the timeout and a potential delay or early shot.
>>>>
>>>
>>> An hour of potential delay mind you.
>>
>> Nope, look at posix-aio-compat. It's an optimization to keep the number
>> worker threads under control.
> 
> The code attempts to sleep for ten seconds, which can turn into an hour
> and ten seconds if the conditions are right.

Yes, but look at what happens then: it is unlikely that the thread will
stay idle so long on a busy system (some request will wake it up earlier
again), and even if that happens, the thread will simply consume a few
resources "a bit" longer.

Jan

Patch

diff --git a/qemu-thread-posix.c b/qemu-thread-posix.c
index 9e1b5fb..cd65df2 100644
--- a/qemu-thread-posix.c
+++ b/qemu-thread-posix.c
@@ -17,6 +17,7 @@ 
 #include <signal.h>
 #include <stdint.h>
 #include <string.h>
+#include <sys/time.h>
 #include "qemu-thread.h"
 
 static void error_exit(int err, const char *msg)
@@ -115,6 +116,28 @@  void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
         error_exit(err, __func__);
 }
 
+/* Returns true if condition was signals, false if timed out. */
+bool qemu_cond_timedwait(QemuCond *cond, QemuMutex *mutex,
+                         unsigned int timeout_ms)
+{
+    struct timespec ts;
+    struct timeval tv;
+    int err;
+
+    gettimeofday(&tv, NULL);
+    ts.tv_sec = tv.tv_sec + timeout_ms / 1000;
+    ts.tv_nsec = tv.tv_usec * 1000 + timeout_ms % 1000;
+    if (ts.tv_nsec > 1000000000) {
+        ts.tv_sec++;
+        ts.tv_nsec -= 1000000000;
+    }
+    err = pthread_cond_timedwait(&cond->cond, &mutex->lock, &ts);
+    if (err && err != ETIMEDOUT) {
+        error_exit(err, __func__);
+    }
+    return err == 0;
+}
+
 void qemu_thread_create(QemuThread *thread,
                        void *(*start_routine)(void*),
                        void *arg, int mode)
diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h
index ee4618e..9f00524 100644
--- a/qemu-thread-posix.h
+++ b/qemu-thread-posix.h
@@ -1,5 +1,6 @@ 
 #ifndef __QEMU_THREAD_POSIX_H
 #define __QEMU_THREAD_POSIX_H 1
+#include <stdbool.h>
 #include "pthread.h"
 
 struct QemuMutex {
@@ -14,4 +15,8 @@  struct QemuThread {
     pthread_t thread;
 };
 
+/* only provided for posix so far */
+bool qemu_cond_timedwait(QemuCond *cond, QemuMutex *mutex,
+                         unsigned int timeout_ms);
+
 #endif