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/* spinlock.h: Header file for cygwin time-sensitive synchronization primitive.
Copyright 2010 Red Hat, Inc.
This file is part of Cygwin.
This software is a copyrighted work licensed under the terms of the
Cygwin license. Please consult the file "CYGWIN_LICENSE" for
details. */
#ifndef _SPINLOCK_H
#define _SPINLOCK_H
#include "ntdll.h"
#define SPINLOCK_WAIT (15000LL * 10000LL)
class spinlock
{
LONG *locker;
LONG val;
LONG setto;
void done (LONG what)
{
if (locker)
{
InterlockedExchange (locker, what);
locker = NULL;
}
}
long long time ()
{
LARGE_INTEGER t;
if (NtQuerySystemTime (&t) == STATUS_SUCCESS)
return get_ll (t);
return 0LL;
}
public:
spinlock (LONG& locktest, LONG wanted_val = 1, LONGLONG timeout = SPINLOCK_WAIT):
locker (&locktest), setto (wanted_val)
{
/* Quick test to see if we're already initialized */
if ((val = locktest) == wanted_val)
locker = NULL;
/* Slightly less quick test to see if we are the first cygwin process */
else if ((val = InterlockedExchange (locker, -1)) == 0)
/* We're armed and dangerous */;
else if (val == wanted_val)
done (val); /* This was initialized while we weren't looking */
else
{
long long then = time ();
/* Loop waiting for some other process to set locktest to something
other than -1, indicating that initialization has finished. Or,
wait a default of 15 seconds for that to happen and, if it doesn't
just grab the lock ourselves. */
while ((val = InterlockedExchange (locker, -1)) == -1
&& (time () - then) < timeout)
yield ();
/* Reset the lock back to wanted_value under the assumption that is
what caused the above loop to kick out. */
if (val == -1)
val = 0; /* Timed out. We'll initialize things ourselves. */
else
done (val); /* Put back whatever was there before, assuming that
it is actually wanted_val. */
}
}
~spinlock () {done (setto);}
operator ULONG () const {return (ULONG) val;}
/* FIXME: This should be handled in a more general fashion, probably by
establishing a linked list of spinlocks which are freed on process exit. */
void multiple_cygwin_problem (const char *w, unsigned m, unsigned v)
{
done (val);
::multiple_cygwin_problem (w, m, v);
}
};
#endif /*_SPINLOCK_H*/
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