On 09/29/2012 03:52 PM, Benjamin Wang (gendwang) wrote:
Hi,
OK. Now I am using JNA to access libvirt. If we add another mutex which used to access “initialized” parameter. This mutex must be pthread_mutex_init firstly and only once.
But it seems that there is no way to change libvirt code. I do it as following:
1.Changing libvirt JNA code in Connect.java
Old Code:
public Connect(String uri) throws LibvirtException {
VCP = libvirt.virConnectOpen(uri);
// Check for an error
processError();
ErrorHandler.processError(Libvirt.INSTANCE);
}
New Code:
public Connect(String uri) throws LibvirtException {
synchronized(this.getClass()) {
VCP = libvirt.virConnectOpen(uri);
}
// Check for an error
processError();
ErrorHandler.processError(Libvirt.INSTANCE);
}
This can make sure only that one thread can execute Connect. For a server application, we only need one time. So the performance is OK
2.Changing libvirt code in libvirt.c
Old Code:
static int initialized = 0;
New Code:
static int volatile initialized = 0;
This can make sure the initialization will be executed once.
Would you give your comments for this solution?
B.R.
Benjamin Wang
As far as I know the operations on |volatile| variable is not atomic, the usage of |volatile| keyword as a portable synchronization mechanism is discouraged by C. But in Java, it is a global ordering on the reads and writes to a volatile variable. So, maybe, your first solution is pretty enough good. Guannan