HP DCE/9000 Version 1.7 Application Development Tools for HP-UX 11.0 Release Note

40 HP DCE 1.7 Application Development Tools Release Note

Developing DCE Applications with HP DCE/ 9000

Notes on Programming with HP DCE

Calling exec() from a DCE Application

Care must be used when calling exec() from a DCE application. HP DCE

Threads sometimes sets open ﬁle descriptors to non-blocking mode, so

that I/O calls block only the calling thread, not the entire process. This

occurs unbeknownst to the application itself. HP provides wrappers for

the exec() family of calls that, among other things, resets ﬁle descriptors

to blocking mode if they were set non-blocking by HP DCE Threads and

not the application.

For ﬁle descriptors that were inherited across fork(), this also has the

effect of resetting the ﬁle descriptor to blocking mode in the parent as

well as the child. If the parent is a threaded program, it can cause the

parent to hang due to a blocking I/O call.

There are two possible work-arounds:

• If the process will not need the open ﬁle descriptor, set the

close-on-exec ﬂag for the ﬁle prior to calling exec(). The ﬁle descriptor

will not be reset in this case.

• Avoid using the exec() wrapper; call exec() directly instead. This is

accomplished by undeﬁning the appropriate macro, for example:

#undef execle.

Note that if the exec() wrapper is circumvented, the new process may

inherit ﬁle descriptors that are unexpectedly set non-blocking; some

signals may be unexpectedly ignored or not ignored; and, if exec() is

called without ﬁrst calling fork(), the new process will probably be killed

by SIGVTALRM as soon as it begins execution.

Process Forking

Process forking from within RPC applications that use the

connection-oriented (TCP/IP) RPC protocol is not supported.

While it is generally safe for an application to perform a fork followed

immediately by an exec(), the following sequence may not work for

TCP/IP RPC programs:

• The TCP/IP RPC process forks.

• The child process tries to use RPC over the TCP/IP protocol before the

exec().