ZeroMQ on z/OS UNIX System Services

ZeroMQ has been successfully built on z/OS, using z/OS UNIX System Services, a certified UNIX environment for the IBM z-series. The build is possible with the shell scripts in this directory, as described below.

Tested build combinations:

• ZeroMQ 4.0.4, using IBM XL C/C++ compiler, as XPLINK in ILP32 mode

• ZeroMQ 4.0.4, using IBM XL C/C++ compiler, as XPLINK in LP64 mode

• ZeroMQ 4.1-git, using IBM XL C/C++ compiler, as XPLINK in ILP32 mode

Other combinations are likely to work, possibly with minor changes, but have not been tested. Both static library and DLL modes have been tested.

There are some minor limitations (detailed below), but all core functionality tests run successfully.

Quickstart: building ZeroMQ on z/OS UNIX System Services

Assuming z/OS UNIX System Services is installed, and the z/OS XL C/C++ compiler suite is installed, ZeroMQ can be built as follows:

• Download and extract ZeroMQ tar file

• Ensure contents of this directory are present at builds/zos within that extracted diretory (eg, zeromq-VERSION/builds/zos/; copy these files in, if not already present, and make sure the shell scripts are executable)

• (Optional) set ZCXXFLAGS for additional compile flags (see below)

• Build libzmq.a static library and libzmq.so dynamic library, with:

  cd zeromq-VERSION
  builds/zos/makelibzmq
  

  or to skip the libzmq.so dynamic library (only building libzmq.a):

  cd zeromq-VERSION
  BUILD_DLL=false
  export BUILD_DLL
  builds/zos/makelibzmq
  

• (Optional, but recommended) build and run the core tests with:

  cd zeromq-VERSION
  builds/zos/maketests
  builds/zos/runtests
  

• To remove built files, to start again (eg, rebuild with different compile/link flags):

  cd zeromq-VERSION
  builds/zos/makeclean
  

There are details on specifying alternative compilation flags below.

Quickstart: using ZeroMQ on z/OS UNIX System Services

Static linking

Install include/*.h somewhere on your compiler include path.

Install src/libzmq.a somewhere on your library search path.

Compile and link application with:

c++ -Wc,xplink -Wl,xplink ... -+ -o myprog myprog.cpp -lzmq

Run with:

./myprog

Dynamic linking

Install include/*.h somewhere on your compiler include path.

Install src/libzmq.so somewhere on your LIBPATH.

Install src/libzmq.x somewhere you can reference for import linking.

Compile and link application:

c++ -Wc,xplink -Wc,dll ... -+ -c -o myprog.o myprog.cpp
c++ -Wl,xplink -o myprog myprog.o /PATH/TO/libzmq.x

Run with:

LIBPATH=/DIR/OF/LIBZMQ.SO:/lib:/usr/lib:...    # if not in default path
export LIBPATH
./myprog

ZeroMQ on z/OS UNIX System Services: Application considerations

z/0S UNIX System Services does not provide a way to block the SIGPIPE signal being generated when a thread writes to a closed socket (compare with other platforms that support the SO_NOSIGPIPE socket option, and/or the MSG_NOSIGNAL flag on send(); z/OS UNIX System Services supports neither).

As a result, applications using ZeroMQ on z/OS UNIX System Services have to expect to encounter SIGPIPE at various times during the use of the library, if sockets are unexpectedly disconnected. Normally SIGPIPE will terminate the application.

A simple solution, if SIGPIPE is not required for normal operation of the application (eg, it is not part of a unix pipeline, the traditional use of SIGPIPE), is to set SIGPIPE to be ignored with code like:

#include <signal.h>
...
signal(SIGPIPE, SIG_IGN);

near the start of the application (eg, before initialising the ZeroMQ library).

If SIGPIPE is required for normal operation it is recommended that the application install a signal handler that flags the signal was received, and allows the application main loop to determine if it was received for one of its own file descriptors -- and ignores it if it none of the applications own file descriptors seems to have changed.

Linking to the libzmq.a static library will pull in substantially all of the library code, which will add about 4MB to the application size (per executable statically linked with ZeroMQ). If this is a significant consideration, use of the DLL version is recommended.

See also ZeroMQ test status on z/OS UNIX System Services below for other caveats.

Setting other compilation flags

Optimisation

To build with optimisation:

• set ZCXXFLAGS to "-O2" before starting build process above

Full debugging symbols

To build with debugging symbols:

• set ZCXXFLAGS to "-g" before starting build process above

64-bit mode (LP64/amode=64)

To build in 64-bit mode:

The default build is ILP32, the default for the IBM XL C/C++ compiler. To build in LP64 mode (64-bit):

• set ZCXXFLAGS to "-Wc,lp64 -Wl,lp64" before starting build

(64-bit mode can be combined with optimisation or debug symbols.)

Combining compilation flags

Other build flags can be used in ZXCCFLAGS if desired. Beware that they are passed through (Bourne) shell expansion, and passed to both the compile and link stages; some experimentation of argument quoting may be required (and arguments requiring parenthesis are particularly complicated).

ZeroMQ test status on z/OS UNIX System Services

As of 2014-07-22, 41 of the 43 tests in the core ZeroMQ test suite pass. There are two tests that are expected to fail:

0. test_abstract_ipc: tests Linux-specific IPC functions, and is expected to fail on non-Linux platforms.

1. test_fork: tests ability to use ZeroMQ both before and after fork (and before exec()); this relies on the ability to use pthreads both before and after fork. On z/OS (and some other UNIX compliant platforms) functions like pthreads_create (used by ZeroMQ) cannot be used after fork and before exec; on z/OS the call after fork fails with ELEMULTITHREADFORK (errno=257) if ZeroMQ was also used before fork. (On z/OS it appears possible to use z/OS after fork, providing it has not been used before fork -- the problem is the two separate initialisations of the threading library, before and after fork, attempting to mix together.) In practice this is unlikely to affect many real-world programs -- most programs use threads or fork without exec, but not both.

2. test_diffserv: tests ability to set IP_TOS (IP Type of Service, or DiffServ) values on sockets. While z/OS UNIX System Services has the preprocessor defines required, it appears not to support the required functionality (call fails with "EDC8109I Protocol not available.")

These three "expected to fail" tests are listed as XFAIL_TESTS, and runtests will still consider the test run successful when they fail as expected. (builds/zos/runtests will automatically skip these "expected to fail" tests if running "all" tests.)

In addition test_security_curve does not do any meaningful testing, as a result of the CURVE support not being compiled in; it requires libsodium, which has not been ported to z/OS UNIX System Services yet.

Multicast (via libpgm) is also not ported or compiled in.

TIPC, a cluster IPC protocol, is only supported on Linux, so it is not compiled