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