On Thu, Jul 26, 2001 at 03:49:58PM -0700, John Baldwin wrote:
> > That does set, not test-and-set. What I want is exactly what the Intel
> > BTS instruction does: atomically test and set a bit.
>
> Unfortunately that is very ia32 specific. The code would be more
> friendly on alpha and ia64 at least if the algo was changed to use
> cmpset on a word instead of test-and-set of a bit.
Another way to look at it is as an IA-32 specific optimization. For
other architectures, we could just use the code you posted earlier.
> If you want, I can look at the code to see where it uses test_and_set()
> to determine how hard that would be. (It might be very easy to do.)
The piece of code which uses it is attached.
-Arun
inline
void acquire_header_lock (volatile POINTER_SIZE_INT *p_header)
{
while (true) {
// Try to grab the lock.
volatile PVOID free_header =(PVOID)(*p_header & BUSY_FORWARDING_BIT_MASK);
volatile PVOID locked_header =(PVOID)((POINTER_SIZE_INT)free_header |
BUSY_FORWARDING_BIT);
assert (locked_header != free_header);
// IA64 - What are the semantics of test_and_set_bit with regards to acq and
rel?
// Hopefully, test_and_set_bit will have acquire semantics and
// test_and_clear_bit will have release semantics.
if ( test_and_set_bit (BUSY_FORWARDING_BIT_OFFSET, (PVOID *)p_header) == 0)
{
assert ((*p_header & BUSY_FORWARDING_BIT) == BUSY_FORWARDING_BIT);
return; // got it this is the only way out.
}
// Try until you get the lock.
while ((*p_header & BUSY_FORWARDING_BIT) == BUSY_FORWARDING_BIT) {
Sleep (0); // Sleep until it might be free.
}
}
}
To Unsubscribe: send mail to [EMAIL PROTECTED]
with "unsubscribe freebsd-hackers" in the body of the message
