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____ _ _
| _ \| |_| |__
| |_) | __| '_ \ ``Only those who attempt
| __/| |_| | | | the absurd can achieve
|_| \__|_| |_| the impossible.''
GNU Pth - The GNU Portable Threads
Version 2.0
Pth is a very portable POSIX/ANSI-C based library for Unix platforms
which provides non-preemptive priority-based scheduling for multiple
threads of execution (aka "multi-threading") inside event-driven
applications. All threads run in the same address space of the server
application, but each thread has its own individual program-counter,
run-time stack, signal mask and errno variable.
The thread scheduling itself is done in a cooperative way, i.e., the
threads are managed and dispatched by a priority- and event-driven
non-preemptive scheduler. The intention is that this way both better
portability and run-time performance is achieved than with preemptive
scheduling. The event facility allows threads to wait until various
types of internal and external events occur, including pending I/O on
file descriptors, asynchronous signals, elapsed timers, pending I/O
on message ports, thread and process termination, and even results of
customized callback functions.
Pth also provides an optional emulation API for POSIX.1c threads
("Pthreads") which can be used for backward compatibility to existing
multi-threaded applications.
NEW IN PTH 2.0
Pth 2.0 provides more strict POSIX.1-2001/SUSv3 compliant wrapper
functions in its high-level I/O API. Most notable, the implementations
of pth_poll(3) and pth_select(3) were completely worked off in order
to achieve POSIX semantics. A Pth variant of the new POSIX pselect(2)
function was introduced, too.
Pth now has support for arbitrary (usually higher than the default)
FD_SETSIZE values to support larger-scale server applications.
A new environment attribute PTH_ATTR_DISPATCHES allows the application
to query the total number of machine context dispatches Pth performed
since the last attribute reset.
Pth's internal machine context implementation is now exported in a
sub-API pth_uctx in order to allow applications to use raw user-space
context switching. This can be used to implement co-routines,
exception handling or even an alternative multi-threading environment
with the help of Pth.
The "hard syscall mapping" functionality was completely rewritten
from scratch. Previously, the internal system call exit points were
based on syscall(2) only. This was problematic because it by-passed
the C library glue code which often performs necessary glue code in
order to call the code in the kernel correctly. Now the internal exit
points are based on a by-system-call dynamically selected combination
of RTLD_NEXT+dlsym(2), dlopen(2)+dlsym(2) and the known syscall(2) (in
this fallback order). This way the "hard syscall mapping" became a lot
more portable and flexible.
Optional support for OSSP ex based exception handling was added which
allows ISO C applications to use fully multi-threading aware ISO C++
style exception handling.
Finally, the Pth build environment was upgraded to be now based on GNU
autoconf 2.57, GNU shtool 1.6.2 and GNU libtool 1.4.3.
MORE INFORMATION
More details about Pth can be found at the following locations from
the GNU and OSSP projects:
o GNU: http://www.gnu.org/software/pth/
o GNU: ftp://ftp.gnu.org/gnu/pth/
o OSSP: http://www.ossp.org/pkg/lib/pth/
o OSSP: ftp://ftp.ossp.org/pkg/lib/pth/
Ralf S. Engelschall
rse@engelschall.com
www.engelschall.com