Re: [dpdk-dev] [PATCH 1/2] eal/windows: add pthread mutex lock

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

Hi Suanming,

There's a remark in patch 2/2 and cover letter:

> If no lock contention
> with the added rte flow level mutex, the mutex only does the atomic
> increasing in pthread_mutex_lock() and decreasing in
> pthread_mutex_unlock(). No futex() syscall will be involved.

Is this property important? To get the described behavior on Windows, you
should've used CRITICAL_SECTION (preferably wrapped in a struct). Mutexes are
kernel objects on Windows and always require syscalls. Otherwise, if mutexes
are sufficient, see a comment inline.

> Add pthread mutex lock as it is needed for the thread safe rte flow
> functions.
> 
> Signed-off-by: Suanming Mou <suanmingm@nvidia.com>
> ---
>  lib/librte_eal/windows/include/pthread.h | 46 ++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/lib/librte_eal/windows/include/pthread.h b/lib/librte_eal/windows/include/pthread.h
> index 99013dc..4e2e0b3 100644
> --- a/lib/librte_eal/windows/include/pthread.h
> +++ b/lib/librte_eal/windows/include/pthread.h
> @@ -28,6 +28,10 @@
>  /* defining pthread_attr_t type on Windows since there is no in Microsoft libc*/
>  typedef void *pthread_attr_t;
>  
> +typedef void *pthread_mutexattr_t;
> +
> +typedef HANDLE pthread_mutex_t;
> +
>  typedef SYNCHRONIZATION_BARRIER pthread_barrier_t;
>  
>  #define pthread_barrier_init(barrier, attr, count) \
> @@ -139,6 +143,48 @@
>  	return 0;
>  }
>  
> +static inline int
> +pthread_mutex_init(pthread_mutex_t *mutex,
> +		   __rte_unused pthread_mutexattr_t *attr)
> +{
> +	*mutex = CreateMutex(NULL, FALSE, NULL);
> +	if (*mutex == NULL) {
> +		RTE_LOG_WIN32_ERR("CreateMutex()");
> +		return -1;
> +	}
> +	return 0;
> +}
> +
> +static inline int
> +pthread_mutex_lock(pthread_mutex_t *mutex)
> +{
> +	if (WaitForSingleObject(*mutex, INFINITE) != WAIT_OBJECT_0) {
> +		RTE_LOG_WIN32_ERR("WaitForSingleObject()");
> +		return -1;

A relevant error code must be returned according to POSIX. Searching the
code for pthread_mutex_lock() calls, I can see that hinic PMD checks for
EOWNERDEAD (corresponding to WAIT_OBJECT_ABANDONED in Windows) and failsafe
PMD supplies return value of pthread_mutex_unlock() to strerror(), i.e. it
should be an errno. Same applies to other functions.

> +	}
> +	return 0;
> +}
> +
> +static inline int
> +pthread_mutex_unlock(pthread_mutex_t *mutex)
> +{
> +	if (!ReleaseMutex(*mutex)) {
> +		RTE_LOG_WIN32_ERR("ReleaseMutex()");
> +		return -1;
> +	}
> +	return 0;
> +}
> +
> +static inline int
> +pthread_mutex_destroy(pthread_mutex_t *mutex)
> +{
> +	if (!CloseHandle(*mutex)) {
> +		RTE_LOG_WIN32_ERR("CloseHandle()");
> +		return -1;
> +	}
> +	return 0;
> +}
> +
>  #ifdef __cplusplus
>  }
>  #endif