Dear SCO Customer,

Support Level Supplement (SLS) PTF7052B, the UnixWare 7.0.1 libthread
Patch, corrects various problems that may be seen by applications that 
link against libthread.

SLS PTF7052B addresses these issues:

1.  The semantics of fork() for multithreaded programs changed in
    UnixWare 7.0.1 to conform with Posix specified behavior.  Fork, instead
    of creating a copy of each application thread, just created a copy of
    the thread that invoked fork.  Applications not prepared for this
    behavior could deadlock if the disappearing threads held critical
    resources.  PTF7052B restores the old behavior for fork.  Applications
    that need the Posix behavior can call fork1() directly or define and
    export a global int called _thread_sys_behavior and set its value to 1.
    This will cause fork to behave like fork1.

2.  Applications that called fork() or fork1() could deadlock if the
    child process performed any operations involving signal disposition
    (sigaction(), sigset(), signal()) before calling exec.

3.  The thread library was incorrectly setting the signal mask used
    while a signal was being handled for handlers set via sigaction().
    The mask did not include those signals masked by the thread before 
    the signal was received.

4.  Applications that invoked lio_listio() could become deadlocked
    under rare circumstances.

5.  Internal thread library data structures could become corrupted in
    applications that created and then killed large numbers of threads.

6.  Calls to sigwait() that selected the signal SIGPOLL might return an
    error code after a successful invocation and incorrectly set the
    signal mask.

7.  Programs that maintain different priorities for multiplexed threads
    can deadlock due to internal lock hierarchy problems in libthread.

8.  High priority threads in a process can be starved resulting in a
    process hang.

9.  Programs that continuously and rapidly suspend/continue a given
    thread can deadlock or dump core.

10. Programs that call signal() with a signal number larger than
    MAXSIG, will corrupt internal libthread data and may dump core.


SLS PTF7052B contains:

        /usr/lib/libthread.so.1
        /usr/lib/libthreadT.so.1
        /usr/lib/libthread.so (link to /usr/lib/libthread.so.1)
        /usr/lib/libthreadT.so (link to /usr/lib/libthreadT.so.1)

The release notes, displayed prior to installation, can be found in:

        /var/sadm/pkg/ptf7052/install/ptf7052.txt



Software Notes and Recommendations
----------------------------------

SLS PTF7052B should only be installed on:

         UnixWare 7.0.1

Note: SLS PTF7052B should be installed prior to installing the Java 
      Development Kit (JDK) 1.1.3w for SCO operating systems.


Hardware Notes and Recommendations
----------------------------------

This SLS is intended for i486, Pentium, Pentium Pro, Pentium II,
and compatible CPUs.



Installation Instructions
-------------------------

1. Download the ptf7052b.Z and ptf7052b.txt files to the /tmp directory on
   your machine.

2. As root, uncompress the file and add the SLS package to your system
   using these commands:

        $ su
        Password: <type your root password>
        # uncompress /tmp/ptf7052b.Z
        # pkgadd -d /tmp/ptf7052b
        # rm /tmp/ptf7052b

3. Reboot the system after installing this SLS package.


Removal Instructions
--------------------

1. As root, remove the SLS package using these commands:

        $ su
        Password: <type your root password>
        # pkgrm ptf7052

2. Reboot the system after removing this SLS package.


If you have questions regarding this SLS, or the product on
which it is installed, please contact your software supplier.