1  /* Single thread optimization, Linux version.
       2     Copyright (C) 2019-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #ifndef _SINGLE_THREAD_H
      20  #define _SINGLE_THREAD_H
      21  
      22  #ifndef __ASSEMBLER__
      23  # include <sys/single_threaded.h>
      24  #endif
      25  
      26  /* The default way to check if the process is single thread is by using the
      27     pthread_t 'multiple_threads' field.  However, for some architectures it is
      28     faster to either use an extra field on TCB or global variables (the TCB
      29     field is also used on x86 for some single-thread atomic optimizations).
      30  
      31     The ABI might define SINGLE_THREAD_BY_GLOBAL to enable the single thread
      32     check to use global variables instead of the pthread_t field.  */
      33  
      34  #if !defined SINGLE_THREAD_BY_GLOBAL || IS_IN (rtld)
      35  # define SINGLE_THREAD_P \
      36    (THREAD_GETMEM (THREAD_SELF, header.multiple_threads) == 0)
      37  #else
      38  # define SINGLE_THREAD_P (__libc_single_threaded_internal != 0)
      39  #endif
      40  
      41  #define RTLD_SINGLE_THREAD_P SINGLE_THREAD_P
      42  
      43  #endif /* _SINGLE_THREAD_H  */