[libvirt] [[RFC] 1/8] Introduce virObjectTrylock()

[Prerna Saxena]

This is a wrapper function that:
(1) Attempts to take a lock on the object.
(2) gracefully returns if the object is already locked.

Signed-off-by: Prerna Saxena <saxenap.ltc at gmail.com>
---
 src/libvirt_private.syms |  1 +
 src/util/virobject.c     | 26 ++++++++++++++++++++++++++
 src/util/virobject.h     |  4 ++++
 src/util/virthread.c     |  5 +++++
 src/util/virthread.h     |  1 +
 5 files changed, 37 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 9243c55..c0ab8b5 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -2362,6 +2362,7 @@ virObjectRWLockableNew;
 virObjectRWLockRead;
 virObjectRWLockWrite;
 virObjectRWUnlock;
+virObjectTrylock;
 virObjectUnlock;
 virObjectUnref;
 
diff --git a/src/util/virobject.c b/src/util/virobject.c
index cfa821c..796ea06 100644
--- a/src/util/virobject.c
+++ b/src/util/virobject.c
@@ -495,6 +495,32 @@ virObjectRWLockWrite(void *anyobj)
 
 
 /**
+ * virObjectTrylock:
+ * @anyobj: any instance of virObjectLockable or virObjectRWLockable
+ *
+ * Attempt to acquire a lock on @anyobj. The lock must be released by
+ * virObjectUnlock.
+ * Returns:
+ *    0: If the lock was successfully taken.
+ *    errno : Indicates error.
+ *
+ * The caller is expected to have acquired a reference
+ * on the object before locking it (eg virObjectRef).
+ * The object must be unlocked before releasing this
+ * reference.
+ */
+int
+virObjectTrylock(void *anyobj)
+{
+    virObjectLockablePtr obj = virObjectGetLockableObj(anyobj);
+
+    if (!obj)
+        return -1;
+
+    return virMutexTrylock(&obj->lock);
+}
+
+/**
  * virObjectUnlock:
  * @anyobj: any instance of virObjectLockable
  *
diff --git a/src/util/virobject.h b/src/util/virobject.h
index ac6cf22..402ea32 100644
--- a/src/util/virobject.h
+++ b/src/util/virobject.h
@@ -124,6 +124,10 @@ void
 virObjectLock(void *lockableobj)
     ATTRIBUTE_NONNULL(1);
 
+int
+virObjectTrylock(void *lockableobj)
+    ATTRIBUTE_NONNULL(1);
+
 void
 virObjectRWLockRead(void *lockableobj)
     ATTRIBUTE_NONNULL(1);
diff --git a/src/util/virthread.c b/src/util/virthread.c
index 6c49515..07b7a3f 100644
--- a/src/util/virthread.c
+++ b/src/util/virthread.c
@@ -89,6 +89,11 @@ void virMutexLock(virMutexPtr m)
     pthread_mutex_lock(&m->lock);
 }
 
+int  virMutexTrylock(virMutexPtr m)
+{
+    return pthread_mutex_trylock(&m->lock);
+}
+
 void virMutexUnlock(virMutexPtr m)
 {
     pthread_mutex_unlock(&m->lock);
diff --git a/src/util/virthread.h b/src/util/virthread.h
index e466d9b..8e3da2c 100644
--- a/src/util/virthread.h
+++ b/src/util/virthread.h
@@ -132,6 +132,7 @@ int virMutexInitRecursive(virMutexPtr m) ATTRIBUTE_RETURN_CHECK;
 void virMutexDestroy(virMutexPtr m);
 
 void virMutexLock(virMutexPtr m);
+int virMutexTrylock(virMutexPtr m);
 void virMutexUnlock(virMutexPtr m);
 
 
-- 
2.9.5