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(&lock_count, -1, 0) != -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 }
--- EOF ---