How to read the manual page for POSIX refering to error codes? - pthreads

Question

I am currently working with pthread and read the documentation from here: Pthread Manual Pthread Join.
However, when I read the pages I see the ERRORS, but not the corresponding return values, which will get returned from pthread_join. So my question is, are the ERRORS ordered in ascending order (since it might be an enumerator)?

Answer 1

Error values such as EDEADLK are macros defined by including the <errno.h> header file.
Example:
#include <pthread.h>
#include <errno.h>
...
int retval = pthread_join( threadID, NULL );
if ( retval == EDEADLK )
{
// error-handling code for deadlock
}
else if ( retval == EINVAL )
{
// error-handling code for invalid thread id
}
else if ( retval == ESRCH )
{
// error-handling code for no such thread id
}
Note that the above code is correct only for Linux, as the only error number specified by POSIX for pthread_join() is EDEADLCK.
Per the POSIX standard for error numbers, (bolded portions particularly relevant to your question):
2.3 Error Numbers
Most functions can provide an error number. The means by which each
function provides its error numbers is specified in its description.
Some functions provide the error number in a variable accessed through
the symbol errno, defined by including the <errno.h> header.
The value of errno should only be examined when it is indicated to
be valid by a function's return value. No function in this volume of
POSIX.1-2008 shall set errno to zero. For each thread of a process,
the value of errno shall not be affected by function calls or
assignments to errno by other threads.
Some functions return an error number directly as the function value. These functions return a value of zero to indicate success.
If more than one error occurs in processing a function call, any one
of the possible errors may be returned, as the order of detection is
undefined.
Implementations may support additional errors not included in this
list, may generate errors included in this list under circumstances
other than those described here, or may contain extensions or
limitations that prevent some errors from occurring.
The ERRORS section on each reference page specifies which error
conditions shall be detected by all implementations ("shall fail") and
which may be optionally detected by an implementation ("may fail"). If
no error condition is detected, the action requested shall be
successful. If an error condition is detected, the action requested
may have been partially performed, unless otherwise stated.
Implementations may generate error numbers listed here under
circumstances other than those described, if and only if all those
error conditions can always be treated identically to the error
conditions as described in this volume of POSIX.1-2008.
Implementations shall not generate a different error number from one
required by this volume of POSIX.1-2008 for an error condition
described in this volume of POSIX.1-2008, but may generate additional
errors unless explicitly disallowed for a particular function.
Each implementation shall document, in the conformance document,
situations in which each of the optional conditions defined in
POSIX.1-2008 is detected. The conformance document may also contain
statements that one or more of the optional error conditions are not
detected.
Certain threads-related functions are not allowed to return an error
code of [EINTR]. Where this applies it is stated in the ERRORS section
on the individual function pages.
The following macro names identify the possible error numbers, in the context of the functions specifically defined in this volume of
POSIX.1-2008; these general descriptions are more precisely defined in
the ERRORS sections of the functions that return them. Only these
macro names should be used in programs, since the actual value of the
error number is unspecified. All values listed in this section shall
be unique, except as noted below. The values for all these macros
shall be found in the <errno.h> header defined in the Base
Definitions volume of POSIX.1-2008. The actual values are unspecified
by this volume of POSIX.1-2008.
[E2BIG]
Argument list too long. The sum of the number of bytes
used by the new process image's argument list and environment
list is greater than the system-imposed limit of {ARG_MAX} bytes.
or:
Lack of space in an output buffer.
or:
Argument is greater than the system-imposed maximum.
[EACCES]
Permission denied. An attempt was made to access a file
in a way forbidden by its file access permissions.
[EADDRINUSE]
Address in use. The specified address is in use.
[EADDRNOTAVAIL]
Address not available. The specified address is not
available from the local system.
[EAFNOSUPPORT]
Address family not supported. The implementation does
not support the specified address family, or the specified
address is not a valid address for the address family
of the specified socket.
[EAGAIN]
Resource temporarily unavailable. This is a temporary
condition and later calls to the same routine may complete
normally.
[EALREADY]
Connection already in progress. A connection request is already
in progress for the specified socket.
.
.
.