Re: [Qemu-devel] [PATCH 3/6] Switch POSIX compat AIO to QEMU abstractions

[Kevin Wolf <kwolf@redhat.com>]

Am 20.09.2011 18:53, schrieb Jan Kiszka:
> Although there is nothing to wrap for non-POSIX here, redirecting thread
> and synchronization services to our core simplifies managements jobs
> like scheduling parameter adjustment. It also frees compat AIO from some
> duplicate code (/wrt qemu-thread).
> 
> CC: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  posix-aio-compat.c |  115 ++++++++++++++-------------------------------------
>  1 files changed, 32 insertions(+), 83 deletions(-)
> 
> diff --git a/posix-aio-compat.c b/posix-aio-compat.c
> index d3c1174..0715aba 100644
> --- a/posix-aio-compat.c
> +++ b/posix-aio-compat.c
> @@ -13,7 +13,6 @@
>  
>  #include <sys/ioctl.h>
>  #include <sys/types.h>
> -#include <pthread.h>
>  #include <unistd.h>
>  #include <errno.h>
>  #include <time.h>
> @@ -27,9 +26,12 @@
>  #include "qemu-common.h"
>  #include "trace.h"
>  #include "block_int.h"
> +#include "qemu-thread.h"
>  
>  #include "block/raw-posix-aio.h"
>  
> +#define AIO_THREAD_IDLE_TIMEOUT 10000 /* 10 s */
> +
>  static void do_spawn_thread(void);
>  
>  struct qemu_paiocb {
> @@ -57,10 +59,9 @@ typedef struct PosixAioState {
>  } PosixAioState;
>  
>  
> -static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
> -static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
> -static pthread_t thread_id;
> -static pthread_attr_t attr;
> +static QemuMutex lock;
> +static QemuCond cond;
> +static QemuThread thread;
>  static int max_threads = 64;
>  static int cur_threads = 0;
>  static int idle_threads = 0;
> @@ -86,39 +87,6 @@ static void die(const char *what)
>      die2(errno, what);
>  }
>  
> -static void mutex_lock(pthread_mutex_t *mutex)
> -{
> -    int ret = pthread_mutex_lock(mutex);
> -    if (ret) die2(ret, "pthread_mutex_lock");
> -}
> -
> -static void mutex_unlock(pthread_mutex_t *mutex)
> -{
> -    int ret = pthread_mutex_unlock(mutex);
> -    if (ret) die2(ret, "pthread_mutex_unlock");
> -}
> -
> -static int cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
> -                           struct timespec *ts)
> -{
> -    int ret = pthread_cond_timedwait(cond, mutex, ts);
> -    if (ret && ret != ETIMEDOUT) die2(ret, "pthread_cond_timedwait");
> -    return ret;
> -}
> -
> -static void cond_signal(pthread_cond_t *cond)
> -{
> -    int ret = pthread_cond_signal(cond);
> -    if (ret) die2(ret, "pthread_cond_signal");
> -}
> -
> -static void thread_create(pthread_t *thread, pthread_attr_t *attr,
> -                          void *(*start_routine)(void*), void *arg)
> -{
> -    int ret = pthread_create(thread, attr, start_routine, arg);
> -    if (ret) die2(ret, "pthread_create");
> -}
> -
>  static ssize_t handle_aiocb_ioctl(struct qemu_paiocb *aiocb)
>  {
>      int ret;
> @@ -311,27 +279,22 @@ static void posix_aio_notify_event(void);
>  
>  static void *aio_thread(void *unused)
>  {
> -    mutex_lock(&lock);
> +    qemu_mutex_lock(&lock);
>      pending_threads--;
> -    mutex_unlock(&lock);
> +    qemu_mutex_unlock(&lock);
>      do_spawn_thread();
>  
>      while (1) {
>          struct qemu_paiocb *aiocb;
> -        ssize_t ret = 0;
> -        qemu_timeval tv;
> -        struct timespec ts;
> -
> -        qemu_gettimeofday(&tv);
> -        ts.tv_sec = tv.tv_sec + 10;
> -        ts.tv_nsec = 0;
> +        bool timed_out = false;
> +        ssize_t ret;
>  
> -        mutex_lock(&lock);
> +        qemu_mutex_lock(&lock);
>  
> -        while (QTAILQ_EMPTY(&request_list) &&
> -               !(ret == ETIMEDOUT)) {
> +        while (QTAILQ_EMPTY(&request_list) && !timed_out) {
>              idle_threads++;
> -            ret = cond_timedwait(&cond, &lock, &ts);
> +            timed_out = qemu_cond_timedwait(&cond, &lock,
> +                                            AIO_THREAD_IDLE_TIMEOUT) != 0;

Maybe I'm confused by too many negations, but isn't this the wrong way
round?

+    err = pthread_cond_timedwait(&cond->cond, &mutex->lock, &ts);
+    if (err && err != ETIMEDOUT) {
+        error_exit(err, __func__);
+    }
+    return err == 0;

So if there was an timeout, qemu_cond_timedwait returns 0 (should it
return a bool? Also documenting the return value wouldn't hurt) and
timed_out becomes false (0 != 0).

Kevin