[libvirt PATCH 05/11] virthread: Introduce virLockGuard

[Ján Tomko]

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 at redhat.com>
>---
> 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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