/*+
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 * Copyright (c) 1999, 2010, 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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+
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#include "precompiled.hpp"+
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#include "runtime/thread.inline.hpp"+
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#include "runtime/threadLocalStorage.hpp"+
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+
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// Map stack pointer (%esp) to thread pointer for faster TLS access+
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//+
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// Here we use a flat table for better performance. Getting current thread+
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// is down to one memory access (read _sp_map[%esp>>12]) in generated code+
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// and two in runtime code (-fPIC code needs an extra load for _sp_map).+
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//+
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// This code assumes stack page is not shared by different threads. It works+
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// in 32-bit VM when page size is 4K (or a multiple of 4K, if that matters).+
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//+
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// Notice that _sp_map is allocated in the bss segment, which is ZFOD+
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// (zero-fill-on-demand). While it reserves 4M address space upfront,+
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// actual memory pages are committed on demand.+
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//+
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// If an application creates and destroys a lot of threads, usually the+
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// stack space freed by a thread will soon get reused by new thread+
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// (this is especially true in NPTL or BsdThreads in fixed-stack mode).+
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// No memory page in _sp_map is wasted.+
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//+
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// However, it's still possible that we might end up populating &+
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// committing a large fraction of the 4M table over time, but the actual+
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// amount of live data in the table could be quite small. The max wastage+
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// is less than 4M bytes. If it becomes an issue, we could use madvise()+
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// with MADV_DONTNEED to reclaim unused (i.e. all-zero) pages in _sp_map.+
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// MADV_DONTNEED on Bsd keeps the virtual memory mapping, but zaps the+
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// physical memory page (i.e. similar to MADV_FREE on Solaris).+
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+
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#ifndef AMD64+
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Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)];+
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#endif // !AMD64+
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+
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void ThreadLocalStorage::generate_code_for_get_thread() {+
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    // nothing we can do here for user-level thread+
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}+
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+
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void ThreadLocalStorage::pd_init() {+
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#ifndef AMD64+
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  assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(),+
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         "page size must be multiple of PAGE_SIZE");+
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#endif // !AMD64+
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}+
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+
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void ThreadLocalStorage::pd_set_thread(Thread* thread) {+
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  os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread);+
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+
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#ifndef AMD64+
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  address stack_top = os::current_stack_base();+
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  size_t stack_size = os::current_stack_size();+
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+
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  for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) {+
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    // pd_set_thread() is called with non-NULL value when a new thread is+
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    // created/attached, or with NULL value when a thread is about to exit.+
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    // If both "thread" and the corresponding _sp_map[] entry are non-NULL,+
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    // they should have the same value. Otherwise it might indicate that the+
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    // stack page is shared by multiple threads. However, a more likely cause+
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    // for this assertion to fail is that an attached thread exited without+
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    // detaching itself from VM, which is a program error and could cause VM+
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    // to crash.+
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    assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL ||+
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           thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT],+
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           "thread exited without detaching from VM??");+
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    _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread;+
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  }+
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#endif // !AMD64+
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}+
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