jdk

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/*
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 * Copyright (c) 2001, 2024, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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#include "precompiled.hpp"
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#include "runtime/atomic.hpp"
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#include "runtime/javaThread.hpp"
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#include "runtime/threadCritical.hpp"
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// OS-includes here
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# include <windows.h>
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# include <winbase.h>
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//
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// See threadCritical.hpp for details of this class.
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//
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static INIT_ONCE initialized = INIT_ONCE_STATIC_INIT;
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static int lock_count = 0;
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static HANDLE lock_event;
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static DWORD lock_owner = 0;
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//
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// Note that Microsoft's critical region code contains a race
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// condition, and is not suitable for use. A thread holding the
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// critical section cannot safely suspend a thread attempting
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// to enter the critical region. The failure mode is that both
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// threads are permanently suspended.
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//
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// I experiemented with the use of ordinary windows mutex objects
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// and found them ~30 times slower than the critical region code.
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//
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static BOOL WINAPI initialize(PINIT_ONCE InitOnce, PVOID Parameter, PVOID *Context) {
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  lock_event = CreateEvent(nullptr, false, true, nullptr);
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  assert(lock_event != nullptr, "unexpected return value from CreateEvent");
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  return true;
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}
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ThreadCritical::ThreadCritical() {
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  InitOnceExecuteOnce(&initialized, &initialize, nullptr, nullptr);
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  DWORD current_thread = GetCurrentThreadId();
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  if (lock_owner != current_thread) {
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    // Grab the lock before doing anything.
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    DWORD ret = WaitForSingleObject(lock_event,  INFINITE);
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    assert(ret != WAIT_FAILED,   "WaitForSingleObject failed with error code: %lu", GetLastError());
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    assert(ret == WAIT_OBJECT_0, "WaitForSingleObject failed with return value: %lu", ret);
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    lock_owner = current_thread;
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  }
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  // Atomicity isn't required. Bump the recursion count.
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  lock_count++;
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}
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ThreadCritical::~ThreadCritical() {
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  assert(lock_owner == GetCurrentThreadId(), "unlock attempt by wrong thread");
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  assert(lock_count >= 0, "Attempt to unlock when already unlocked");
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  lock_count--;
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  if (lock_count == 0) {
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    // We're going to unlock
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    lock_owner = 0;
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    // No lost wakeups, lock_event stays signaled until reset.
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    DWORD ret = SetEvent(lock_event);
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    assert(ret != 0, "unexpected return value from SetEvent");
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  }
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}
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