Embedding D Shared Library in WSGI Web Server

[John McFarlane via Digitalmars-d-learn]

Hi,

I've written a modest shared library in D that I'd like to call 
directly from a Python web server (Linux/OS X, Apache, WSGI, 
Pyramid). I can call it reliably from within Python unit tests 
but on a running server, the library causes a SIGSEGV as soon as 
I try anything as complicated as a writeln call. Under Linux, 
I've tried using Pyd, CFFI and ctypes to bind the native .so to 
Python with the same result. I've tried calling 
Runtime.initialize();from an init function on server startup and 
from the D function being called as part of the web request. I've 
even tried writing a shim in C to make these calls and call 
through to the D.

I've compiled with DMD and GDC with a variety of switches. 
Currently my build command looks like:

     dmd ./d/*.d -version=library -release -shared -O -inline 
-defaultlib=libphobos2.so -fPIC -oflibgusteau.so

The extern(C) function takes a string and returns a string. I've 
tried holding onto a pointer to the returned string and passing 
in an adequately sized byte array from Python. Smaller strings 
seem to cause a crash with lower probability but typically the 
input and output strings are a few KB in size and consistently 
crash. I taken measures to ensure that they are correctly encoded 
and null terminated. I've also tried disabling the GC, calling 
terminate on function exit (after copying result into received 
buffer) and various other measures in an attempt to get something 
working.

I'm guessing that the web server spawns/relies on a thread or 
process for each request and I've read that runtime 
initialization should be invoked from the main thread. Does this 
always mean the first thread that was created on process start up 
or does it just have to be consistent? If calling from a thread 
other than the one used to initialize, is that a problem? Are 
other threads created when GC is invoked which might last past 
the extern function being called and if so, can I prevent this by 
controlling collection explicitly?

Thanks, John