Re: [PATCHES] UPDATED UnixWare Threads Patch.

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

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