SpinLock.cc

Go to the documentation of this file.
00001 /*
00002  * IMPORTANT: READ BEFORE DOWNLOADING, COPYING, INSTALLING OR USING. By
00003  * downloading, copying, installing or using the software you agree to
00004  * this license. If you do not agree to this license, do not download,
00005  * install, copy or use the software.
00006  * 
00007  * Intel Open Source License 
00008  * 
00009  * Copyright (c) 2004 Intel Corporation. All rights reserved. 
00010  * 
00011  * Redistribution and use in source and binary forms, with or without
00012  * modification, are permitted provided that the following conditions are
00013  * met:
00014  * 
00015  *   Redistributions of source code must retain the above copyright
00016  *   notice, this list of conditions and the following disclaimer.
00017  * 
00018  *   Redistributions in binary form must reproduce the above copyright
00019  *   notice, this list of conditions and the following disclaimer in the
00020  *   documentation and/or other materials provided with the distribution.
00021  * 
00022  *   Neither the name of the Intel Corporation nor the names of its
00023  *   contributors may be used to endorse or promote products derived from
00024  *   this software without specific prior written permission.
00025  *  
00026  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
00027  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
00028  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
00029  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE INTEL OR
00030  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
00031  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
00032  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
00033  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
00034  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
00035  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
00036  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00037  */
00038 
00039 #include "SpinLock.h"
00040 #include "../debug/StackTrace.h"
00041 
00042 namespace oasys {
00043 
00044 bool     SpinLock::warn_on_contention_(true);
00045 #ifndef NDEBUG
00046 atomic_t SpinLock::total_spins_(0);
00047 atomic_t SpinLock::total_yields_(0);
00048 #endif
00049 
00050 int
00051 SpinLock::lock(const char* lock_user)
00052 {
00053     if (is_locked_by_me()) {
00054         lock_count_.value++;
00055         return 0;
00056     }
00057 
00058     atomic_incr(&lock_waiters_);
00059     
00060     int nspins = 0;
00061     (void)nspins;
00062     while (atomic_cmpxchg32(&lock_count_, 0, 1) != 0)
00063     {
00064         Thread::spin_yield();
00065         
00066 #ifndef NDEBUG
00067         atomic_incr(&total_spins_);
00068         if (warn_on_contention_ && ++nspins > 1000000) {
00069             fprintf(stderr,
00070                     "warning: spin lock held by %s reached spin limit\n",
00071                     lock_holder_name_);
00072             StackTrace::print_current_trace(false);
00073             nspins = 0;
00074         }
00075 #endif
00076     }
00077 
00078     atomic_decr(&lock_waiters_);
00079 
00080     ASSERT(lock_count_.value == 1);
00081 
00082     lock_holder_      = Thread::current();
00083     lock_holder_name_ = lock_user;
00084 
00085     return 0;
00086 };
00087 
00088 int
00089 SpinLock::unlock()
00090 {
00091     ASSERT(is_locked_by_me());
00092 
00093     if (lock_count_.value > 1) {
00094         lock_count_.value--;
00095         return 0;
00096     }
00097 
00098     lock_holder_      = 0;
00099     lock_holder_name_ = 0;
00100     lock_count_.value = 0;
00101     
00102     if (lock_waiters_.value != 0) {
00103 #ifndef NDEBUG
00104         atomic_incr(&total_yields_);
00105 #endif
00106         Thread::spin_yield();
00107     }
00108 
00109 
00110     return 0;
00111 };
00112  
00113 int
00114 SpinLock::try_lock(const char* lock_user)
00115 {
00116     if (is_locked_by_me()) {
00117         lock_count_.value++;
00118         return 0;
00119     }
00120 
00121     int got_lock = atomic_cmpxchg32(&lock_count_, 0, 1);
00122     
00123     if (got_lock) {
00124         ASSERT(lock_holder_ == 0);
00125 
00126         lock_holder_      = Thread::current();
00127         lock_holder_name_ = lock_user;
00128         
00129         return 0; // success
00130         
00131     } else {
00132         return 1; // already locked
00133     }
00134 };
00135 
00136 } // namespace oasys

Generated on Fri Dec 22 14:48:00 2006 for DTN Reference Implementation by  doxygen 1.5.1