1 /* |
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2 * Copyright (c) 1999, 2015, 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/thread.inline.hpp" |
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27 #include "runtime/threadLocalStorage.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 // No memory page in _sp_map is wasted. |
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45 // |
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46 // However, it's still possible that we might end up populating & |
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47 // committing a large fraction of the 4M table over time, but the actual |
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48 // amount of live data in the table could be quite small. The max wastage |
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49 // is less than 4M bytes. If it becomes an issue, we could use madvise() |
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50 // with MADV_DONTNEED to reclaim unused (i.e. all-zero) pages in _sp_map. |
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51 // MADV_DONTNEED on Linux keeps the virtual memory mapping, but zaps the |
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52 // physical memory page (i.e. similar to MADV_FREE on Solaris). |
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53 |
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54 #if !defined(AMD64) && !defined(MINIMIZE_RAM_USAGE) |
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55 Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)]; |
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56 |
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57 void ThreadLocalStorage::generate_code_for_get_thread() { |
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58 // nothing we can do here for user-level thread |
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59 } |
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60 |
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61 void ThreadLocalStorage::pd_init() { |
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62 assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(), |
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63 "page size must be multiple of PAGE_SIZE"); |
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64 } |
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65 |
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66 void ThreadLocalStorage::pd_set_thread(Thread* thread) { |
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67 os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread); |
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68 address stack_top = os::current_stack_base(); |
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69 size_t stack_size = os::current_stack_size(); |
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70 |
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71 for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) { |
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72 // pd_set_thread() is called with non-NULL value when a new thread is |
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73 // created/attached, or with NULL value when a thread is about to exit. |
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74 // If both "thread" and the corresponding _sp_map[] entry are non-NULL, |
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75 // they should have the same value. Otherwise it might indicate that the |
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76 // stack page is shared by multiple threads. However, a more likely cause |
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77 // for this assertion to fail is that an attached thread exited without |
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78 // detaching itself from VM, which is a program error and could cause VM |
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79 // to crash. |
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80 assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL || |
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81 thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT], |
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82 "thread exited without detaching from VM??"); |
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83 _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread; |
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84 } |
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85 } |
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86 #else |
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87 |
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88 void ThreadLocalStorage::generate_code_for_get_thread() { |
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89 // nothing we can do here for user-level thread |
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90 } |
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91 |
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92 void ThreadLocalStorage::pd_init() { |
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93 } |
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94 |
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95 void ThreadLocalStorage::pd_set_thread(Thread* thread) { |
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96 os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread); |
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97 } |
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98 #endif // !AMD64 && !MINIMIZE_RAM_USAGE |
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