mulle-kybernetik-tv / mulleapxsexample

🚩 Apache Module based on MulleObjC

MulleAPXSExample

Works on Ubuntu Linux with apache2. This page is a collection of random thoughts. Read it all, if you want to reproduce this.

Research Findings

The apache daemon loads shared libraries with RTLD_GLOBAL. That means, that the global universe variable is shared between modules. Therefore only one global variable (not hashtable) universe exists and the modules share the libMulleObjC-standalone.so loaded by the first extension.

Care must be taken, that classes have differing names.

How to reproduce

Build as explained in Memo: Apache/Libtool/ObjC then also build the second example in src2 likewise. Also install the objc_example2.* files in ./apache2 into the mods-enabled folder of /etc/apache2 alongside the objc_example.* files.

Then check http://localhost/objc-example and http://localhost/objc-example2

Feature: Named Universes

This is done in by specifying -DOTHER_CFLAGS=-fobjc-universename=myuniverse.

Tweaks used to build the first universe

1. Set MULLE_CRAFT_MULLE_OBJC_MAKE_FLAGS to -DSTANDALONE=ON, so that MulleObjC gets build as a shared library, but not the constituent static libraries.
2. Specified a craftinfo for MulleObjC so that OTHER_CFLAGS is set to -fobjc-universename="vfl1848"
3. Otherwise do as explained way below, and don't forget to copy the .so file.

Tweaks used to build the second universe

1. remove the old stuff with mulle-sde clean all
2. Specified a craftinfo for MulleObjC so that OTHER_CFLAGS is set to -fobjc-universename="vfl1849" (a different universename)
3. Change the soname of the standalone library to libMulleObjC2-standalone.so
4. rename built standalone library to libMulleObjC2-standalone.so and copy it to /usr/lib
5. Go into src2 and make and make install

See: mulle-sde environment list

Memo: Apache/Libtool/ObjC

Libtool can not properly deal with the --whole-archive flag as researched by reading this and this mailthread.

This makes it not feasible to link ObjC code statically into a Libtooling environment such as an apache module. But linking a shared library to a C apache module is not a problem.

Build MulleObjC with STANDALONE.

Note: use tweak idea above

mulle-sde -v craft buildorder --release -- -DSTANDALONE=ON
sudo cp -a ../dependency/lib/libMulleObjC-standalone.so /usr/lib

Since we are going to install into /usr/lib a LD_RUN_PATH seems pointless.

Now build and install the module:

cd src
make
sudo make install
sudo apache2ctl restart

Again a LD_LIBRARY_PATH would be pointless, because the apache daemon doesn't seem to pick it up. Or we would have to edit /etc/apache2/envvars.

Install dependencies

This is a partial mulle-sde project.

mulle-sde MulleAPXSExample

Now you can let mulle-sde fetch the required dependencies and build the project for you:

mulle-sde craft buildorder

Build

Venture into the src directory and run make.

Read mulle_objc_example.c for more information.

Install

apache2 contains configuration files that need to be added after sudo make install

Debug

How to debug inside the apache.

$ sudo -s
# . /etc/apache2/envvars
# MULLE_SDE_TRACE_UNIVERSE=YES \
  MULLE_SDE_TRACE_ENABLED=YES \
  gdb /usr/sbin/apache2
gdb> set verbose on
gdb> run -X