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Change the description of errno to match the thread-aware implementation

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from 3.0 on. With 3.0 being a major release, now is a good time to do
this.
This commit is contained in:
John Birrell 1998-04-30 09:49:59 +00:00
parent 1b46cb523d
commit 26dac90648
1 changed files with 6 additions and 32 deletions
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38
lib/libc/sys/intro.2
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@ -50,46 +50,20 @@ their error returns, and other common definitions and concepts.
Nearly all of the system calls provide an error number referenced via
the external identifier errno. This identifier is defined in
.Aq Pa sys/errno.h
for non-threaded programs as:
.Pp
.Dl extern int errno;
.Pp
and for threaded programs as:
as
.Pp
.Dl extern int * __error();
.Dl #define errno (* __error())
.Pp
A threaded program must be compiled with
.Va _THREAD_SAFE
defined so that the preprocessor will output the appropriate errno
definition to the compiler. Failure to do so will mean that error
variables will not be thread specific.
.Pp
The threaded library implementation of
The
.Va __error()
returns a pointer to a field in the thread specific structure for
threads other than the initial thread. For the initial thread,
function returns a pointer to a field in the thread specific structure for
threads other than the initial thread. For the initial thread and
non-threaded processes,
.Va __error()
returns a pointer to a global
.Va errno
variable that is compatible with that used by non-threaded programs.
This allows the initial thread to call functions in libraries which have
not been compiled with
.Va _THREAD_SAFE .
Programmers should ensure that threads other than the initial thread only
call functions in libraries that have been compiled with
.Va _THREAD_SAFE .
.Pp
Programmers should include
.Aq Pa sys/errno.h
to obtain the definition of
.Va errno
rather than coding the definition as an external reference directly. It is
planned that the
.Va extern int errno
definition will eventually be replaced by the threaded definition so that
all libraries will have a thread-aware treatment of
.Va errno .
variable that is compatible with the previous definition.
.Pp
When a system call detects an error,
it returns an integer value