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3960
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1 /*
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2 * Copyright (c) 1999, 2010, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24
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25 #include "precompiled.hpp"
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26 #include "runtime/threadLocalStorage.hpp"
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27 #include "thread_bsd.inline.hpp"
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28
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29 // Map stack pointer (%esp) to thread pointer for faster TLS access
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30 //
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31 // Here we use a flat table for better performance. Getting current thread
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32 // is down to one memory access (read _sp_map[%esp>>12]) in generated code
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33 // and two in runtime code (-fPIC code needs an extra load for _sp_map).
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34 //
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35 // This code assumes stack page is not shared by different threads. It works
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36 // in 32-bit VM when page size is 4K (or a multiple of 4K, if that matters).
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37 //
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38 // Notice that _sp_map is allocated in the bss segment, which is ZFOD
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39 // (zero-fill-on-demand). While it reserves 4M address space upfront,
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40 // actual memory pages are committed on demand.
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41 //
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42 // If an application creates and destroys a lot of threads, usually the
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43 // stack space freed by a thread will soon get reused by new thread
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44 // (this is especially true in NPTL or BsdThreads in fixed-stack mode).
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45 // No memory page in _sp_map is wasted.
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46 //
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47 // However, it's still possible that we might end up populating &
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48 // committing a large fraction of the 4M table over time, but the actual
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49 // amount of live data in the table could be quite small. The max wastage
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50 // is less than 4M bytes. If it becomes an issue, we could use madvise()
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51 // with MADV_DONTNEED to reclaim unused (i.e. all-zero) pages in _sp_map.
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52 // MADV_DONTNEED on Bsd keeps the virtual memory mapping, but zaps the
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53 // physical memory page (i.e. similar to MADV_FREE on Solaris).
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54
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55 #ifndef AMD64
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56 Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)];
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57 #endif // !AMD64
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58
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59 void ThreadLocalStorage::generate_code_for_get_thread() {
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60 // nothing we can do here for user-level thread
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61 }
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62
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63 void ThreadLocalStorage::pd_init() {
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64 #ifndef AMD64
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65 assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(),
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66 "page size must be multiple of PAGE_SIZE");
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67 #endif // !AMD64
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68 }
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69
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70 void ThreadLocalStorage::pd_set_thread(Thread* thread) {
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71 os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread);
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72
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73 #ifndef AMD64
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74 address stack_top = os::current_stack_base();
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75 size_t stack_size = os::current_stack_size();
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76
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77 for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) {
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78 // pd_set_thread() is called with non-NULL value when a new thread is
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79 // created/attached, or with NULL value when a thread is about to exit.
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80 // If both "thread" and the corresponding _sp_map[] entry are non-NULL,
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81 // they should have the same value. Otherwise it might indicate that the
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82 // stack page is shared by multiple threads. However, a more likely cause
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83 // for this assertion to fail is that an attached thread exited without
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84 // detaching itself from VM, which is a program error and could cause VM
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85 // to crash.
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86 assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL ||
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87 thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT],
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88 "thread exited without detaching from VM??");
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89 _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread;
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90 }
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91 #endif // !AMD64
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92 }
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