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 
  59 void ThreadLocalStorage::generate_code_for_get_thread() {
  60     // nothing we can do here for user-level thread
  61 }
  62 
  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 
  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 }