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