Impressum threadCritical_windows.cpp Sprache: unbekannt

/*
* Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/

#include "precompiled.hpp"
#include "runtime/atomic.hpp"
#include "runtime/javaThread.hpp"
#include "runtime/threadCritical.hpp"

// OS-includes here
# include <windows.h>
# include <winbase.h>

//
// See threadCritical.hpp for details of this class.
//

static INIT_ONCE initialized = INIT_ONCE_STATIC_INIT;
static int lock_count = 0;
static HANDLE lock_event;
static DWORD lock_owner = 0;

//
// Note that Microsoft's critical region code contains a race
// condition, and is not suitable for use. A thread holding the
// critical section cannot safely suspend a thread attempting
// to enter the critical region. The failure mode is that both
// threads are permanently suspended.
//
// I experiemented with the use of ordinary windows mutex objects
// and found them ~30 times slower than the critical region code.
//

static BOOL WINAPI initialize(PINIT_ONCE InitOnce, PVOID Parameter, PVOID *Context) {
  lock_event = CreateEvent(NULL, false, true, NULL);
  assert(lock_event != NULL, "unexpected return value from CreateEvent");
  return true;
}

ThreadCritical::ThreadCritical() {
  InitOnceExecuteOnce(&initialized, &initialize, NULL, NULL);

  DWORD current_thread = GetCurrentThreadId();
  if (lock_owner != current_thread) {
    // Grab the lock before doing anything.
    DWORD ret = WaitForSingleObject(lock_event,  INFINITE);
    assert(ret == WAIT_OBJECT_0, "unexpected return value from WaitForSingleObject");
    lock_owner = current_thread;
  }
  // Atomicity isn't required. Bump the recursion count.
  lock_count++;
}

ThreadCritical::~ThreadCritical() {
  assert(lock_owner == GetCurrentThreadId(), "unlock attempt by wrong thread");
  assert(lock_count >= 0, "Attempt to unlock when already unlocked");

  lock_count--;
  if (lock_count == 0) {
    // We're going to unlock
    lock_owner = 0;
    // No lost wakeups, lock_event stays signaled until reset.
    DWORD ret = SetEvent(lock_event);
    assert(ret != 0, "unexpected return value from SetEvent");
  }
}

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Impressum threadCritical_windows.cpp Sprache: unbekannt

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