1 /* 2 * Copyright (c) 1999, 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "runtime/thread.inline.hpp" 27 #include "runtime/threadLocalStorage.hpp" 28 29 // Map stack pointer (%esp) to thread pointer for faster TLS access 30 // 31 // Here we use a flat table for better performance. Getting current thread 32 // is down to one memory access (read _sp_map[%esp>>12]) in generated code 33 // and two in runtime code (-fPIC code needs an extra load for _sp_map). 34 // 35 // This code assumes stack page is not shared by different threads. It works 36 // in 32-bit VM when page size is 4K (or a multiple of 4K, if that matters). 37 // 38 // Notice that _sp_map is allocated in the bss segment, which is ZFOD 39 // (zero-fill-on-demand). While it reserves 4M address space upfront, 40 // actual memory pages are committed on demand. 41 // 42 // If an application creates and destroys a lot of threads, usually the 43 // stack space freed by a thread will soon get reused by new thread. 44 // No memory page in _sp_map is wasted. 45 // 46 // However, it's still possible that we might end up populating & 47 // committing a large fraction of the 4M table over time, but the actual 48 // amount of live data in the table could be quite small. The max wastage 49 // is less than 4M bytes. If it becomes an issue, we could use madvise() 50 // with MADV_DONTNEED to reclaim unused (i.e. all-zero) pages in _sp_map. 51 // MADV_DONTNEED on Linux keeps the virtual memory mapping, but zaps the 52 // physical memory page (i.e. similar to MADV_FREE on Solaris). 53 54 #if !defined(AMD64) && !defined(MINIMIZE_RAM_USAGE) 55 Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)]; 56 57 void ThreadLocalStorage::generate_code_for_get_thread() { 58 // nothing we can do here for user-level thread 59 } 60 61 void ThreadLocalStorage::pd_init() { 62 assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(), 63 "page size must be multiple of PAGE_SIZE"); 64 } 65 66 void ThreadLocalStorage::pd_set_thread(Thread* thread) { 67 os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread); 68 address stack_top = os::current_stack_base(); 69 size_t stack_size = os::current_stack_size(); 70 71 for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) { 72 // pd_set_thread() is called with non-NULL value when a new thread is 73 // created/attached, or with NULL value when a thread is about to exit. 74 // If both "thread" and the corresponding _sp_map[] entry are non-NULL, 75 // they should have the same value. Otherwise it might indicate that the 76 // stack page is shared by multiple threads. However, a more likely cause 77 // for this assertion to fail is that an attached thread exited without 78 // detaching itself from VM, which is a program error and could cause VM 79 // to crash. 80 assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL || 81 thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT], 82 "thread exited without detaching from VM??"); 83 _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread; 84 } 85 } 86 #else 87 88 void ThreadLocalStorage::generate_code_for_get_thread() { 89 // nothing we can do here for user-level thread 90 } 91 92 void ThreadLocalStorage::pd_init() { 93 } 94 95 void ThreadLocalStorage::pd_set_thread(Thread* thread) { 96 os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread); 97 } 98 #endif // !AMD64 && !MINIMIZE_RAM_USAGE