Re: [libvirt PATCH 05/11] virthread: Introduce virLockGuard

[Ján Tomko <jtomko@xxxxxxxxxx>]

On a Wednesday in 2021, Tim Wiederhake wrote:
> Locks a virMutex on creation and unlocks it in its destructor.
>
> Typical usage:
>
>    void function(virMutex *m)
>    {
>        vir_g_autoptr(virLockGuard) lock = virLockGuardNew(m);

Since the developer does not need to refer to the 'lock' variable,
wrapping it in a VIR_MUTEX_LOCK macro would be more convenient.

(Even though it would not be usable outside the variable declaration
section, due to our enabled warnings)

Jano

>        /* `m` is locked, and released automatically on scope exit */
>
>        ...
>        while (expression) {
>            vir_g_autoptr(virLockGuard) lock2 = virLockGuardNew(...);
>            /* similar */
>        }
>    }
>
> Signed-off-by: Tim Wiederhake <twiederh@xxxxxxxxxx>
> ---
> src/libvirt_private.syms |  3 +++
> src/util/virthread.c     | 26 ++++++++++++++++++++++++++
> src/util/virthread.h     | 10 ++++++++++
> 3 files changed, 39 insertions(+)
>
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index fa11ee3df5..d8170a59af 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -3367,6 +3367,9 @@ virCondInit;
> virCondSignal;
> virCondWait;
> virCondWaitUntil;
> +virLockGuardFree;
> +virLockGuardNew;
> +virLockGuardUnlock;
> virMutexDestroy;
> virMutexInit;
> virMutexInitRecursive;
> diff --git a/src/util/virthread.c b/src/util/virthread.c
> index e89c1a09fb..a5a948985f 100644
> --- a/src/util/virthread.c
> +++ b/src/util/virthread.c
> @@ -96,6 +96,32 @@ void virMutexUnlock(virMutex *m)
>     pthread_mutex_unlock(&m->lock);
> }
>
> +virLockGuard *virLockGuardNew(virMutex *m)
> +{
> +    virLockGuard *l = g_new0(virLockGuard, 1);
> +    l->mutex = m;
> +
> +    virMutexLock(l->mutex);
> +    return l;
> +}
> +
> +void virLockGuardFree(virLockGuard *l)
> +{
> +    if (!l)
> +        return;
> +
> +    virLockGuardUnlock(l);
> +    g_free(l);
> +}
> +
> +void virLockGuardUnlock(virLockGuard *l)
> +{
> +    if (!l)
> +        return;
> +
> +    virMutexUnlock(g_steal_pointer(&l->mutex));
> +}
> +
>
> int virRWLockInit(virRWLock *m)
> {
> diff --git a/src/util/virthread.h b/src/util/virthread.h
> index 55c8263ae6..b394dbd226 100644
> --- a/src/util/virthread.h
> +++ b/src/util/virthread.h
> @@ -31,6 +31,11 @@ struct virMutex {
>     pthread_mutex_t lock;
> };
>
> +typedef struct virLockGuard virLockGuard;
> +struct virLockGuard {
> +    virMutex *mutex;
> +};
> +
> typedef struct virRWLock virRWLock;
> struct virRWLock {
>     pthread_rwlock_t lock;
> @@ -121,6 +126,11 @@ void virMutexLock(virMutex *m);
> void virMutexUnlock(virMutex *m);
>
>
> +virLockGuard *virLockGuardNew(virMutex *m);
> +void virLockGuardFree(virLockGuard *l);
> +void virLockGuardUnlock(virLockGuard *l);
> +G_DEFINE_AUTOPTR_CLEANUP_FUNC(virLockGuard, virLockGuardFree);
> +
> int virRWLockInit(virRWLock *m) G_GNUC_WARN_UNUSED_RESULT;
> void virRWLockDestroy(virRWLock *m);
>
> --
> 2.31.1

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