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 }