XrdSysSemWait.hh

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00001 #ifndef __SYS_SEMWAIT__
00002 #define __SYS_SEMWAIT__
00003 
00004 /******************************************************************************/
00005 /*                       X r d S y s S e m W a i t                            */
00006 /*                                                                            */
00007 /* Author: Fabrizio Furano (INFN, 2005)                                       */
00008 /*                                                                            */
00009 /* This file is part of the XRootD software suite.                            */
00010 /*                                                                            */
00011 /* XRootD is free software: you can redistribute it and/or modify it under    */
00012 /* the terms of the GNU Lesser General Public License as published by the     */
00013 /* Free Software Foundation, either version 3 of the License, or (at your     */
00014 /* option) any later version.                                                 */
00015 /*                                                                            */
00016 /* XRootD is distributed in the hope that it will be useful, but WITHOUT      */
00017 /* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or      */
00018 /* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public       */
00019 /* License for more details.                                                  */
00020 /*                                                                            */
00021 /* You should have received a copy of the GNU Lesser General Public License   */
00022 /* along with XRootD in a file called COPYING.LESSER (LGPL license) and file  */
00023 /* COPYING (GPL license).  If not, see <http://www.gnu.org/licenses/>.        */
00024 /*                                                                            */
00025 /* The copyright holder's institutional names and contributor's names may not */
00026 /* be used to endorse or promote products derived from this software without  */
00027 /* specific prior written permission of the institution or contributor.       */
00028 /*                                                                            */
00029 /* A counting semaphore with timed out wait primitive                         */
00030 /******************************************************************************/
00031 
00032 #include "XrdSys/XrdSysPthread.hh"
00033 
00034 class XrdSysSemWait {
00035  public:
00036 
00037    int  CondWait() {
00038 
00039       int rc = 0;
00040       // Wait until the sempahore value is positive. This will not be starvation
00041       // free is the OS implements an unfair mutex;
00042       // Returns 0 if signalled, non-0 if would block
00043       //
00044 
00045       semVar.Lock();
00046       if (semVal > 0) semVal--;
00047       else {
00048          rc = 1;
00049       }
00050 
00051       semVar.UnLock();
00052 
00053       return rc;
00054 
00055    };
00056    
00057    void Post() {
00058       // Add one to the semaphore counter. If we the value is > 0 and there is a
00059       // thread waiting for the sempagore, signal it to get the semaphore.
00060       //
00061       semVar.Lock();
00062 
00063       if (semWait > 0) {
00064          semVar.Signal();
00065          semWait--;
00066       }
00067       else
00068          semVal++;
00069       
00070       semVar.UnLock();
00071    };
00072    
00073    void Wait()   {
00074       // Wait until the sempahore value is positive. This will not be starvation
00075       // free is the OS implements an unfair mutex;
00076       //
00077 
00078       semVar.Lock();
00079       if (semVal > 0) semVal--;
00080       else {
00081          semWait++;
00082          semVar.Wait();
00083       }
00084 
00085       semVar.UnLock();
00086 
00087    };
00088 
00089    int Wait(int secs)  {
00090       int rc = 0;
00091       // Wait until the sempahore value is positive. This will not be starvation
00092       // free is the OS implements an unfair mutex;
00093       // Returns 0 if signalled, non-0 if timeout
00094       //
00095 
00096       semVar.Lock();
00097       if (semVal > 0) semVal--;
00098       else {
00099          semWait++;
00100          rc = semVar.Wait(secs);
00101          if (rc) semWait--;
00102       }
00103 
00104       semVar.UnLock();
00105 
00106       return rc;
00107    };
00108 
00109    XrdSysSemWait(int semval=1,const char *cid=0) : semVar(0, cid) {
00110       semVal = semval; semWait = 0;
00111    }
00112 
00113    ~XrdSysSemWait() {}
00114 
00115 private:
00116 
00117 XrdSysCondVar semVar;
00118 int           semVal;
00119 int           semWait;
00120 };
00121 
00122 
00123 
00124 #endif

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