118 lines
4.0 KiB
TeX
118 lines
4.0 KiB
TeX
@node Reentrancy
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@chapter Reentrancy
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@cindex reentrancy
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Reentrancy is a characteristic of library functions which allows multiple
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processes to use the same address space with assurance that the values stored
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in those spaces will remain constant between calls. Cygnus's implementation
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of the library functions ensures that
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whenever possible, these library functions are reentrant. However,
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there are some functions that can not be trivially made reentrant.
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Hooks have been provided to allow you to use these functions in a fully
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reentrant fashion.
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@findex _reent
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@findex reent.h
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@cindex reentrancy structure
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These hooks use the structure @code{_reent} defined in @file{reent.h}.
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A variable defined as @samp{struct _reent} is called a @dfn{reentrancy
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structure}. All functions which must manipulate global information are
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available in two versions. The first version has the usual name, and
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uses a single global instance of the reentrancy structure. The second
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has a different name, normally formed by prepending @samp{_} and
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appending @samp{_r}, and takes a pointer to the particular reentrancy
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structure to use.
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For example, the function @code{fopen} takes two arguments, @var{file}
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and @var{mode}, and uses the global reentrancy structure. The function
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@code{_fopen_r} takes the arguments, @var{struct_reent}, which is a
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pointer to an instance of the reentrancy structure, @var{file}
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and @var{mode}.
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There are two versions of @samp{struct _reent}, a normal one and one
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for small memory systems, controlled by the @code{_REENT_SMALL}
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definition from the (automatically included) @file{<sys/config.h>}.
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@cindex global reentrancy structure
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@findex _impure_ptr
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Each function which uses the global reentrancy structure uses the global
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variable @code{_impure_ptr}, which points to a reentrancy structure.
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This means that you have two ways to achieve reentrancy. Both require
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that each thread of execution control initialize a unique global
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variable of type @samp{struct _reent}:
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@enumerate
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@item
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@cindex extra argument, reentrant fns
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Use the reentrant versions of the library functions, after initializing
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a global reentrancy structure for each process. Use the pointer to this
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structure as the extra argument for all library functions.
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@item
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Ensure that each thread of execution control has a pointer to its own
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unique reentrancy structure in the global variable @code{_impure_ptr},
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and call the standard library subroutines.
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@end enumerate
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@cindex list of reentrant functions
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@cindex reentrant function list
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The following functions are provided in both reentrant
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and non-reentrant versions.
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@example
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@exdent @emph{Equivalent for errno variable:}
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_errno_r
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@exdent @emph{Locale functions:}
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_localeconv_r _setlocale_r
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@exdent @emph{Equivalents for stdio variables:}
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_stdin_r _stdout_r _stderr_r
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@page
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@exdent @emph{Stdio functions:}
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_fdopen_r _perror_r _tempnam_r
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_fopen_r _putchar_r _tmpnam_r
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_getchar_r _puts_r _tmpfile_r
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_gets_r _remove_r _vfprintf_r
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_iprintf_r _rename_r _vsnprintf_r
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_mkstemp_r _snprintf_r _vsprintf_r
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_mktemp_t _sprintf_r
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@exdent @emph{Signal functions:}
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_init_signal_r _signal_r
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_kill_r __sigtramp_r
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_raise_r
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@exdent @emph{Stdlib functions:}
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_calloc_r _mblen_r _setenv_r
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_dtoa_r _mbstowcs_r _srand_r
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_free_r _mbtowc_r _strtod_r
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_getenv_r _memalign_r _strtol_r
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_mallinfo_r _mstats_r _strtoul_r
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_malloc_r _putenv_r _system_r
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_malloc_r _rand_r _wcstombs_r
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_malloc_stats_r _realloc_r _wctomb_r
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@exdent @emph{String functions:}
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_strdup_r _strtok_r
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@exdent @emph{System functions:}
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_close_r _link_r _unlink_r
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_execve_r _lseek_r _wait_r
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_fcntl_r _open_r _write_r
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_fork_r _read_r
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_fstat_r _sbrk_r
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_gettimeofday_r _stat_r
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_getpid_r _times_r
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@ifset STDIO64
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@exdent @emph{Additional 64-bit I/O System functions:}
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_fstat64_r _lseek64_r _open64_r
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@end ifset
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@exdent @emph{Time function:}
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_asctime_r
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@end example
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