I posted this to patches, but the hackers list should be aware of the
current thread library issues.


Bruce Momjian wrote:
OK, I have applied the attached patch.

Here is the comment I have added to the thread.c file:

* Threading sometimes requires specially-named versions of functions
* that return data in static buffers, like strerror_r() instead of
* strerror(). Other operating systems use pthread_setspecific()
* and pthread_getspecific() internally to allow standard library
* functions to return static data to threaded applications.
* Additional confusion exists because many operating systems that
* use pthread_setspecific/pthread_getspecific() also have *_r versions
* of standard library functions for compatibility with operating systems
* that require them. However, internally, these *_r functions merely
* call the thread-safe standard library functions.
* For example, BSD/OS 4.3 uses Bind 8.2.3 for getpwuid(). Internally,
* getpwuid() calls pthread_setspecific/pthread_getspecific() to return
* static data to the caller in a thread-safe manner. However, BSD/OS
* also has getpwuid_r(), which merely calls getpwuid() and shifts
* around the arguments to match the getpwuid_r() function declaration.
* Therefore, while BSD/OS has getpwuid_r(), it isn't required. It also
* doesn't have strerror_r(), so we can't fall back to only using *_r
* functions for threaded programs.
* The current setup is to assume either all standard functions are
* thread-safe (NEED_REENTRANT_FUNC_NAMES=no), or the operating system
* requires reentrant function names (NEED_REENTRANT_FUNC_NAMES=yes).

As an additional data point, here is a README comment from Bind 8.2.3:

Thread Safety:

It is possible for a thread safe program to be altered to call the
underlying interface (rather than the standard getXbyY() stubs) and get some
reentrance capabilities. Note that the underlying libraries (which we call)
are not all thread-safe, for example, the YP and DNS resolvers. A lot more
work will need to be done before we have full thread safety. But we believe
that the native API for this system does not impose any reentrancy problems.
We don't use global or static variables anywhere except in the getXbyY() stubs.

Here is Bind's gethostbyname_r:

gethostbyname_r(const char *name, struct hostent *hptr, HOST_R_ARGS) {
struct hostent *he = gethostbyname(name);


if (he == NULL)
return (HOST_R_BAD);

return (copy_hostent(he, hptr, HOST_R_COPY));

As you can see, it merely calls gethostbyname() and adjusts to return
the proper values.

I removed the pre-POSIX getpwuid_r function call and added the POSIX
one. If we need the pre-POSIX one, we can add it with a configure
test, but I would rather find out if someone needs it first. The
original thread patch that was posted had only the pre-POSIX version of
the function, and I am not sure why the didn't include the POSIX one
too, or use that instead of the pre-POSIX one.

There are also a few stylistic function declaration cleanups.

The unixware optimizer changes have already been applied.
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073

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postedAug 14, '03 at 9:25p
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