1 /*
2 * Copyright (c) 1999, 2010, 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 // (this is especially true in NPTL or BsdThreads in fixed-stack mode).
45 // No memory page in _sp_map is wasted.
46 //
47 // However, it's still possible that we might end up populating &
48 // committing a large fraction of the 4M table over time, but the actual
49 // amount of live data in the table could be quite small. The max wastage
50 // is less than 4M bytes. If it becomes an issue, we could use madvise()
51 // with MADV_DONTNEED to reclaim unused (i.e. all-zero) pages in _sp_map.
52 // MADV_DONTNEED on Bsd keeps the virtual memory mapping, but zaps the
53 // physical memory page (i.e. similar to MADV_FREE on Solaris).
54
55 #ifndef AMD64
56 Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)];
57 #endif // !AMD64
58
generate_code_for_get_thread()59 void ThreadLocalStorage::generate_code_for_get_thread() {
60 // nothing we can do here for user-level thread
61 }
62
pd_init()63 void ThreadLocalStorage::pd_init() {
64 #ifndef AMD64
65 assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(),
66 "page size must be multiple of PAGE_SIZE");
67 #endif // !AMD64
68 }
69
pd_set_thread(Thread * thread)70 void ThreadLocalStorage::pd_set_thread(Thread* thread) {
71 os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread);
72
73 #ifndef AMD64
74 address stack_top = os::current_stack_base();
75 size_t stack_size = os::current_stack_size();
76
77 for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) {
78 // pd_set_thread() is called with non-NULL value when a new thread is
79 // created/attached, or with NULL value when a thread is about to exit.
80 // If both "thread" and the corresponding _sp_map[] entry are non-NULL,
81 // they should have the same value. Otherwise it might indicate that the
82 // stack page is shared by multiple threads. However, a more likely cause
83 // for this assertion to fail is that an attached thread exited without
84 // detaching itself from VM, which is a program error and could cause VM
85 // to crash.
86 assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL ||
87 thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT],
88 "thread exited without detaching from VM??");
89 _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread;
90 }
91 #endif // !AMD64
92 }
93