void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure) {
internal::AtomicWord state = internal::Acquire_Load(once);
// Fast path. The provided closure was already executed.
if (state == ONCE_STATE_DONE) {
return;
}
// The closure execution did not complete yet. The once object can be in one
// of the two following states:
// - UNINITIALIZED: We are the first thread calling this function.
// - EXECUTING_CLOSURE: Another thread is already executing the closure.
//
// First, try to change the state from UNINITIALIZED to EXECUTING_CLOSURE
// atomically.
state = internal::Acquire_CompareAndSwap(
once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_CLOSURE);
if (state == ONCE_STATE_UNINITIALIZED) {
// We are the first thread to call this function, so we have to call the
// closure.
closure->Run();
internal::Release_Store(once, ONCE_STATE_DONE);
} else {
// Another thread has already started executing the closure. We need to
// wait until it completes the initialization.
while (state == ONCE_STATE_EXECUTING_CLOSURE) {
// Note that futex() could be used here on Linux as an improvement.
SchedYield();
state = internal::Acquire_Load(once);
}
}
}
static NTSTATUS
GnttabRevokeForeignAccess(
IN PINTERFACE Interface,
IN PXENBUS_GNTTAB_CACHE Cache,
IN BOOLEAN Locked,
IN PXENBUS_GNTTAB_ENTRY Entry
)
{
PXENBUS_GNTTAB_CONTEXT Context = Interface->Context;
volatile SHORT *flags;
ULONG Attempt;
NTSTATUS status;
ASSERT3U(Entry->Magic, ==, XENBUS_GNTTAB_ENTRY_MAGIC);
ASSERT3U(Entry->Reference, >=, XENBUS_GNTTAB_RESERVED_ENTRY_COUNT);
ASSERT3U(Entry->Reference, <, (Context->FrameIndex + 1) * XENBUS_GNTTAB_ENTRY_PER_FRAME);
flags = (volatile SHORT *)&Context->Table[Entry->Reference].flags;
Attempt = 0;
while (Attempt++ < 100) {
uint16_t Old;
uint16_t New;
Old = *flags;
Old &= ~(GTF_reading | GTF_writing);
New = Old & ~GTF_permit_access;
if (InterlockedCompareExchange16(flags, New, Old) == Old)
break;
SchedYield();
}
status = STATUS_UNSUCCESSFUL;
if (Attempt == 100)
goto fail1;
RtlZeroMemory(&Context->Table[Entry->Reference],
sizeof (grant_entry_v1_t));
RtlZeroMemory(&Entry->Entry,
sizeof (grant_entry_v1_t));
XENBUS_CACHE(Put,
&Context->CacheInterface,
Cache->Cache,
Entry,
Locked);
return STATUS_SUCCESS;
fail1:
Error("fail1 (%08x)\n", status);
return status;
}
static NTSTATUS
GnttabRevokeForeignAccess(
IN PXENBUS_GNTTAB_CONTEXT Context,
IN PXENBUS_GNTTAB_CACHE Cache,
IN BOOLEAN Locked,
IN PXENBUS_GNTTAB_DESCRIPTOR Descriptor
)
{
grant_entry_v1_t *Entry;
volatile SHORT *Flags;
ULONG Attempt;
NTSTATUS status;
ASSERT3U(Descriptor->Magic, ==, GNTTAB_DESCRIPTOR_MAGIC);
ASSERT3U(Descriptor->Reference, >=, GNTTAB_RESERVED_ENTRY_COUNT);
ASSERT3U(Descriptor->Reference, <, (Context->FrameIndex + 1) * GNTTAB_ENTRY_PER_FRAME);
Entry = &Context->Entry[Descriptor->Reference];
Flags = (volatile SHORT *)&Entry->flags;
Attempt = 0;
while (Attempt++ < 100) {
uint16_t Old;
uint16_t New;
Old = *Flags;
Old &= ~(GTF_reading | GTF_writing);
New = Old & ~GTF_permit_access;
if (InterlockedCompareExchange16(Flags, New, Old) == Old)
break;
SchedYield();
}
status = STATUS_UNSUCCESSFUL;
if (Attempt == 100)
goto fail1;
RtlZeroMemory(Entry, sizeof (grant_entry_v1_t));
RtlZeroMemory(&Descriptor->Entry, sizeof (grant_entry_v1_t));
CACHE(Put,
Context->CacheInterface,
Cache->Cache,
Descriptor,
Locked);
return STATUS_SUCCESS;
fail1:
Error("fail1 (%08x)\n", status);
return status;
}
int main()
{
SchedSet(NULL, NULL, SCHED_RR, NULL);
SyncTypeCreate(_NTO_SYNC_SEM, &Semaphore, NULL); // initial count: 0
ThreadCreate(NULL, Thread1, NULL, NULL);
ThreadCreate(NULL, Thread1, NULL, NULL);
sleep(3);
ThreadCreate(NULL, Thread2, NULL, NULL);
SchedYield();
sleep(11);
return(0);
}
/*-
*-----------------------------------------------------------------------
* Reset --
* Tell DIX to reset itself when SIG_TERM is received.
*
* Results:
* None.
*
* Side Effects:
* clientsDoomed is set 1 and the dispatched is told to yield...
*
*-----------------------------------------------------------------------
*/
int
Reset()
{
clientsDoomed = 1;
SchedYield();
}