1 /* 2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "runtime/atomic.hpp" 27 #include "runtime/thread.inline.hpp" 28 #include "runtime/threadCritical.hpp" 29 30 // OS-includes here 31 # include <windows.h> 32 # include <winbase.h> 33 34 // 35 // See threadCritical.hpp for details of this class. 36 // 37 38 static bool initialized = false; 39 static volatile int lock_count = -1; 40 static HANDLE lock_event; 41 static DWORD lock_owner = -1; 42 43 // 44 // Note that Microsoft's critical region code contains a race 45 // condition, and is not suitable for use. A thread holding the 46 // critical section cannot safely suspend a thread attempting 47 // to enter the critical region. The failure mode is that both 48 // threads are permanently suspended. 49 // 50 // I experiemented with the use of ordinary windows mutex objects 51 // and found them ~30 times slower than the critical region code. 52 // 53 54 ThreadCritical::ThreadCritical() { 55 DWORD current_thread = GetCurrentThreadId(); 56 57 if (lock_owner != current_thread) { 58 // Grab the lock before doing anything. 59 while (Atomic::cmpxchg(0, &lock_count, -1) != -1) { 60 if (initialized) { 61 DWORD ret = WaitForSingleObject(lock_event, INFINITE); 62 assert(ret == WAIT_OBJECT_0, "unexpected return value from WaitForSingleObject"); 63 } 64 } 65 66 // Make sure the event object is allocated. 67 if (!initialized) { 68 // Locking will not work correctly unless this is autoreset. 69 lock_event = CreateEvent(NULL, false, false, NULL); 70 initialized = true; 71 } 72 73 assert(lock_owner == -1, "Lock acquired illegally."); 74 lock_owner = current_thread; 75 } else { 76 // Atomicity isn't required. Bump the recursion count. 77 lock_count++; 78 } 79 80 assert(lock_owner == GetCurrentThreadId(), "Lock acquired illegally."); 81 } 82 83 ThreadCritical::~ThreadCritical() { 84 assert(lock_owner == GetCurrentThreadId(), "unlock attempt by wrong thread"); 85 assert(lock_count >= 0, "Attempt to unlock when already unlocked"); 86 87 if (lock_count == 0) { 88 // We're going to unlock 89 lock_owner = -1; 90 lock_count = -1; 91 // No lost wakeups, lock_event stays signaled until reset. 92 DWORD ret = SetEvent(lock_event); 93 assert(ret != 0, "unexpected return value from SetEvent"); 94 } else { 95 // Just unwinding a recursive lock; 96 lock_count--; 97 } 98 }