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annotate src/os_cpu/linux_x86/vm/threadLS_linux_x86.cpp @ 1713:7fcd5f39bd7a
Merge
author | johnc |
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date | Sat, 14 Aug 2010 00:47:52 -0700 |
parents | c18cbe5936b8 |
children | f95d63e2154a |
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0 | 1 /* |
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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. |
0 | 22 * |
23 */ | |
24 | |
25 #include "incls/_precompiled.incl" | |
26 #include "incls/_threadLS_linux_x86.cpp.incl" | |
27 | |
28 // Map stack pointer (%esp) to thread pointer for faster TLS access | |
29 // | |
30 // Here we use a flat table for better performance. Getting current thread | |
31 // is down to one memory access (read _sp_map[%esp>>12]) in generated code | |
32 // and two in runtime code (-fPIC code needs an extra load for _sp_map). | |
33 // | |
34 // This code assumes stack page is not shared by different threads. It works | |
35 // in 32-bit VM when page size is 4K (or a multiple of 4K, if that matters). | |
36 // | |
37 // Notice that _sp_map is allocated in the bss segment, which is ZFOD | |
38 // (zero-fill-on-demand). While it reserves 4M address space upfront, | |
39 // actual memory pages are committed on demand. | |
40 // | |
41 // If an application creates and destroys a lot of threads, usually the | |
42 // stack space freed by a thread will soon get reused by new thread | |
43 // (this is especially true in NPTL or LinuxThreads in fixed-stack mode). | |
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 #ifndef AMD64 | |
55 Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)]; | |
56 #endif // !AMD64 | |
57 | |
58 void ThreadLocalStorage::generate_code_for_get_thread() { | |
59 // nothing we can do here for user-level thread | |
60 } | |
61 | |
62 void ThreadLocalStorage::pd_init() { | |
63 #ifndef AMD64 | |
64 assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(), | |
65 "page size must be multiple of PAGE_SIZE"); | |
66 #endif // !AMD64 | |
67 } | |
68 | |
69 void ThreadLocalStorage::pd_set_thread(Thread* thread) { | |
70 os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread); | |
71 | |
72 #ifndef AMD64 | |
73 address stack_top = os::current_stack_base(); | |
74 size_t stack_size = os::current_stack_size(); | |
75 | |
76 for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) { | |
77 // pd_set_thread() is called with non-NULL value when a new thread is | |
78 // created/attached, or with NULL value when a thread is about to exit. | |
79 // If both "thread" and the corresponding _sp_map[] entry are non-NULL, | |
80 // they should have the same value. Otherwise it might indicate that the | |
81 // stack page is shared by multiple threads. However, a more likely cause | |
82 // for this assertion to fail is that an attached thread exited without | |
83 // detaching itself from VM, which is a program error and could cause VM | |
84 // to crash. | |
85 assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL || | |
86 thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT], | |
87 "thread exited without detaching from VM??"); | |
88 _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread; | |
89 } | |
90 #endif // !AMD64 | |
91 } |