DCE for the HP e3000 (B3821-90003)

46 Chapter5
Programming with Kernel Threads
Writing Threaded Applications
Writing Threaded Applications
Useful hints on writing multi-threaded DCE applications:
• All DCE applications are multi-threaded — DCE runtime software
is multi-threaded and all DCE applications are multi-threaded; even
if the application code itself does not explicitly create threads.
• Using non-thread-safe libraries — When making calls to libraries
which are not known to be specifically thread-safe, a locking scheme
needs to be provided by the application, For example,
non-thread-safe routines 1 and 2 make a call to routine A (also
non-thread-safe), if routines 1 and 2 use different mutexes to lock
their calls to routine A, then routines 1 and 2 can both get into
routine A at the same time (violating the programmer’s attempt to
make the calls thread-safe).
• Using fork() in a threaded application — fork() is not allowed
from a threaded task.
• environ is a process-wide resource — Programmers must
coordinate threads that use the putenv() and getenv() interfaces
to change and read environ.
• Signal mask: A thread-specific resource — If one thread manipulates
the signal mask, it only affects signals that a specific thread is
interested in.
• Handling synchronous terminating signals — The default behavior
of OSF DCE 1.0.2 is to translate synchronous terminating signals
into exceptions. If the exception is not caught, the thread that caused
the exception is terminated. Any thread that goes through the
terminate code causes the entire task to be terminated.
• Establish synchronous signal handlers using sigaction() — It is
used to establish handlers for synchronous signals on an individual
thread basis only.
• Asynchronous signals — There is no supported mechanism for
establishing signal handlers for asynchronous signals on MPE/iX.
• Cancelling threads blocked on a system call — The HP e3000 Kernel
Threads provide a cancellation facility that enables one thread to
terminate another. The canceled thread normally terminates at a
well-defined point. Terminating a thread that is blocked while
executing system code is not possible on MPE/iX; only threads
executing non-system code may be canceled.
• Using waitpid() — The waitpid() routine allows the parent
thread to specify which child it cares about by specifying its PID.
This call only works for the initial thread; because children created
by any thread within the task are considered children of the whole