[libvirt-users] Thread-safety issues with vbox driver ?

[Jean-Baptiste Rouault]

Hi,

I'm experiencing weird things with the vbox driver when using multiple threads.
Following is the snippet of code I experience problems with

/*****************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <libvirt/libvirt.h>

void *create_and_destroy(void *arg)
{
    virDomainPtr dom = (virDomainPtr)arg;

    char buf[VIR_UUID_STRING_BUFLEN];
    virDomainGetUUIDString(dom, buf);
    
    if (virDomainCreate(dom) != 0) {
        printf("failed to start %s\n", buf);
        goto end;
    }
    printf("%s started\n", buf);

    if (virDomainDestroy(dom) != 0) {
        printf("failed to destroy %s\n", buf);
    }
    printf("%s destroyed\n", buf);

end:
    virDomainFree(dom);
    pthread_exit(NULL);
}

int main(int argc, char **argv)
{
    virConnectPtr conn = virConnectOpen("vbox:///session");
    
    int i;
    int count = virConnectNumOfDefinedDomains(conn);
    char **names = malloc(count * sizeof(char *));
    virConnectListDefinedDomains(conn, names, count);
    virDomainPtr *doms = malloc(count * sizeof(virDomainPtr));
    for (i = 0 ; i < count ; ++i) {
        doms[i] = virDomainLookupByName(conn, names[i]);
    }

    pthread_t *threads = malloc(count * sizeof(pthread_t));
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

    for (i = 0 ; i < count ; ++i) {
        pthread_create(&threads[i], &attr, create_and_destroy, (void *)doms[i]);
    }

    pthread_attr_destroy(&attr);
    for (i = 0 ; i < count ; ++i) {
        pthread_join(threads[i], NULL);
    }

    virConnectClose(conn);

    pthread_exit(NULL);
}
/************************************************/

Here is the output of the program with 2 defined domains:
> libvir: VBOX error : operation failed: OpenRemoteSession/LaunchVMProcess failed, domain can't be started
> failed to start c538c89a-70da-42ab-a88a-5aeb15698c12
> 034cf837-abe7-4c48-8373-0ddcf480d416 started
> 034cf837-abe7-4c48-8373-0ddcf480d416 destroyed

Sometimes the first domain really fails to start, but sometimes it starts correctly but libvirt reports
an error. Sometimes domains aren't destroyed but libvirt reports no error at all.
If there is only one domain, no problem occurs at all. I also tried the same code (ie with multiple domains)
but with only one thread and it works well.

I managed to reproduce these issues with libvirt 0.9.4, 0.9.7, using VirtualBox 4.0 and 4.1.

-- 
Jean-Baptiste ROUAULT
Ingénieur R&D - diateam : Architectes de l'information
Phone : +33 (0)9 53 16 02 70 Fax : +33 (0)2 98 050 051