/*

 * Copyright (c) 1999, 2010, 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/thread.inline.hpp"

#include "runtime/threadLocalStorage.hpp"

// Map stack pointer (%esp) to thread pointer for faster TLS access

//

// Here we use a flat table for better performance. Getting current thread

// is down to one memory access (read _sp_map[%esp>>12]) in generated code

// and two in runtime code (-fPIC code needs an extra load for _sp_map).

//

// This code assumes stack page is not shared by different threads. It works

// in 32-bit VM when page size is 4K (or a multiple of 4K, if that matters).

//

// Notice that _sp_map is allocated in the bss segment, which is ZFOD

// (zero-fill-on-demand). While it reserves 4M address space upfront,

// actual memory pages are committed on demand.

//

// If an application creates and destroys a lot of threads, usually the

// stack space freed by a thread will soon get reused by new thread

// (this is especially true in NPTL or LinuxThreads in fixed-stack mode).

// No memory page in _sp_map is wasted.

//

// However, it's still possible that we might end up populating &

// committing a large fraction of the 4M table over time, but the actual

// amount of live data in the table could be quite small. The max wastage

// is less than 4M bytes. If it becomes an issue, we could use madvise()

// with MADV_DONTNEED to reclaim unused (i.e. all-zero) pages in _sp_map.

// MADV_DONTNEED on Linux keeps the virtual memory mapping, but zaps the

// physical memory page (i.e. similar to MADV_FREE on Solaris).

#if !defined(AMD64) && !defined(MINIMIZE_RAM_USAGE)

Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)];

void ThreadLocalStorage::generate_code_for_get_thread() {

    // nothing we can do here for user-level thread

}

void ThreadLocalStorage::pd_init() {

  assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(),

         "page size must be multiple of PAGE_SIZE");

}

void ThreadLocalStorage::pd_set_thread(Thread* thread) {

  os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread);

  address stack_top = os::current_stack_base();

  size_t stack_size = os::current_stack_size();

  for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) {

    // pd_set_thread() is called with non-NULL value when a new thread is

    // created/attached, or with NULL value when a thread is about to exit.

    // If both "thread" and the corresponding _sp_map[] entry are non-NULL,

    // they should have the same value. Otherwise it might indicate that the

    // stack page is shared by multiple threads. However, a more likely cause

    // for this assertion to fail is that an attached thread exited without

    // detaching itself from VM, which is a program error and could cause VM

    // to crash.

    assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL ||

           thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT],

           "thread exited without detaching from VM??");

    _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread;

  }

}

#else

void ThreadLocalStorage::generate_code_for_get_thread() {

    // nothing we can do here for user-level thread

}

void ThreadLocalStorage::pd_init() {

}

void ThreadLocalStorage::pd_set_thread(Thread* thread) {

  os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread);

}

#endif // !AMD64 && !MINIMIZE_RAM_USAGE