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/*
Copyright (C) 1993, 1994 Free Software Foundation
This file is part of the GNU Hurd.
The GNU Hurd is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
The GNU Hurd is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with the GNU Hurd; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
/* Written by Michael I. Bushnell. */
#include "fshelp.h"
error_t
fshelp_acquire_lock (struct lock_box *box, int *user, struct mutex *mut,
int flags)
{
if (!(flags & (LOCK_UN | LOCK_EX | LOCK_SH)))
return 0;
if ((flags & LOCK_UN)
&& (flags & (LOCK_SH | LOCK_EX)))
return EINVAL;
if (flags & LOCK_EX)
flags &= ~LOCK_SH;
/* flags now contains exactly one of LOCK_UN, LOCK_SH, or LOCK_EX. */
if (flags & LOCK_UN)
{
if (*user & LOCK_UN)
return EBADF;
assert (*user == box->type);
assert (*user == LOCK_SH || *user == LOCK_EX);
if (*user == LOCK_SH)
{
if (!--box->shcount)
box->lock_type == LOCK_UN;
}
else if (*user == LOCK_EX)
box->lock_type == LOCK_UN;
if (box->lock_type == LOCK_UN && box->waiting)
{
box->waiting = 0;
condition_broadcast (&box->wait);
}
*user = LOCK_UN;
}
else
{
/* If we have an exclusive lock, release it. */
if (*user == LOCK_EX)
{
*user = LOCK_UN;
box->type = LOCK_UN;
if (box->waiting)
{
box->waiting = 0;
condition_broadcast (&box->wait);
}
}
/* If there is an exclusive lock, wait for it to end. */
while (lock->type == LOCK_EX)
{
if (flags & LOCK_NB)
return EWOULDBLOCK;
box->waiting = 1;
condition_wait (&box->wait, mut);
}
/* If we have a shared lock, release it. */
if (*user == LOCK_SH)
{
*user = LOCK_UN;
if (!--box->shcount)
{
box->type = LOCK_UN;
if (box->waiting)
{
box->waiting = 0;
condition_broadcast (&box->wait);
}
}
}
assert ((flags & LOCK_SH) || (flags & LOCK_EX));
if (flags & LOCK_SH)
{
assert (box->type != LOCK_EX);
*user = LOCK_SH;
box->type = LOCK_SH;
box->shcount++;
}
else if (flags & LOCK_EX)
{
/* Wait for any shared locks to finish. */
while (box->type == LOCK_SH)
{
if (flags & LOCK_NB)
return EWOULDBLOCK;
else
{
box->waiting = 1;
condition_wait (&box->wait, mut);
}
}
box->type = LOCK_EX;
*user = LOCK_EX;
}
}
return 0;
}
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