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XrdSysXSLock.cc
Go to the documentation of this file.
/******************************************************************************/
/* */
/* X r d S y s X S L o c k . c c */
/* */
/* (c) 2003 by the Board of Trustees of the Leland Stanford, Jr., University */
/* All Rights Reserved */
/* Produced by Andrew Hanushevsky for Stanford University under contract */
/* DE-AC02-76-SFO0515 with the Department of Energy */
/* */
/* This file is part of the XRootD software suite. */
/* */
/* XRootD is free software: you can redistribute it and/or modify it under */
/* the terms of the GNU Lesser General Public License as published by the */
/* Free Software Foundation, either version 3 of the License, or (at your */
/* option) any later version. */
/* */
/* XRootD 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 Lesser General Public */
/* License for more details. */
/* */
/* You should have received a copy of the GNU Lesser General Public License */
/* along with XRootD in a file called COPYING.LESSER (LGPL license) and file */
/* COPYING (GPL license). If not, see <http://www.gnu.org/licenses/>. */
/* */
/* The copyright holder's institutional names and contributor's names may not */
/* be used to endorse or promote products derived from this software without */
/* specific prior written permission of the institution or contributor. */
/******************************************************************************/
#include "XrdSys/XrdSysHeaders.hh"
#include "XrdSys/XrdSysXSLock.hh"
/******************************************************************************/
/* D e s t r u c t o r */
/******************************************************************************/
XrdSysXSLock::~XrdSysXSLock()
{
// Prevent usage while destroying object but make sure no one else is using it
//
LockContext.Lock();
if (cur_count || shr_wait || exc_wait)
{LockContext.UnLock();
abort();
}
LockContext.UnLock();
}
/******************************************************************************/
/* L o c k */
/******************************************************************************/
void XrdSysXSLock::Lock(const XrdSysXS_Type usage)
{
// Serialize access to this object
//
LockContext.Lock();
// This loop continues until we can acquire the resource. We are gauranteed
// to eventually acquire it regardless of the unblocking order.
//
while(cur_count)
{
// If usage is compatible with current usage get the lock right away
//
if (usage == xs_Shared && cur_usage == xs_Shared && !exc_wait) break;
// Indicate that we are waiting
//
if (usage == xs_Shared) shr_wait++;
else exc_wait++;
// Usage is not compatible. We must wait for current lock mode to end
//
LockContext.UnLock();
if (usage == xs_Shared) WantShr.Wait();
else WantExc.Wait();
LockContext.Lock();
}
// We obtained the right to use this object
//
cur_usage = usage;
cur_count++;
LockContext.UnLock();
}
/******************************************************************************/
/* U n L o c k */
/******************************************************************************/
void XrdSysXSLock::UnLock(const XrdSysXS_Type usage)
{
// Serialize access to our data
//
LockContext.Lock();
// Make sure that the lock is currently being used
//
if (!cur_count)
{LockContext.UnLock();
std::cerr << "XSLock: Attempt to unlock inactive lock." <<std::endl;
throw "XSLock: unlocking inactive lock.";
}
// Verify that usage is correct
//
if (usage && cur_usage != usage)
{LockContext.UnLock();
std::cerr << "XSLock: Incorrect unlock usage - "
<< (cur_usage == xs_Shared ? "shr" : "exc") << "!="
<< ( usage == xs_Shared ? "shr" : "exc") << std::endl;
throw "XSLock: invalid unlock usage specified.";
}
// Unlock the current object. If no locks exist then check if we can let another
// thread use this object. The logic is tricky but we are trying to avoid
// starvation in an environment that has no thread ordering.
//
cur_count--;
if (!cur_count)
if (exc_wait && (toggle || !shr_wait))
{toggle = 0; WantExc.Post(); exc_wait--;}
else {while(shr_wait) {WantShr.Post(); shr_wait--;}
toggle = 1;}
else if (!toggle) {while(shr_wait) {WantShr.Post(); shr_wait--;}
toggle = 1;}
LockContext.UnLock();
}
usage
void usage()
Definition XrdClReplay.cc:1072
XrdSysHeaders.hh
XrdSysXSLock.hh
XrdSysXS_Type
XrdSysXS_Type
Definition XrdSysXSLock.hh:38
xs_Shared
@ xs_Shared
Definition XrdSysXSLock.hh:38
XrdSysXSLock::Lock
void Lock(const XrdSysXS_Type usage)
Definition XrdSysXSLock.cc:55
XrdSysXSLock::UnLock
void UnLock(const XrdSysXS_Type usage=xs_None)
Definition XrdSysXSLock.cc:95
XrdSysXSLock::~XrdSysXSLock
~XrdSysXSLock()
Definition XrdSysXSLock.cc:38