| /* |
| * Copyright (c) 1999, 2015, 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. |
| // 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 |