zmachine | Z-machine interpreter in Go | Interpreter library

for url in splitarr[x]: creates an iterator for the sequence in splitarr[x]. It doesn't matter that you increment x later - the iterator is already built. Since you have a print in there, its very likely that all of the threads will grab x when its still zero and iterate the same sequence.

One solution is to pass incrementing values to task1 via the args argument in threading.Thread. But a thread pool is even easier.

I am aware that there is a lot of debate around recursive makefiles.

I'm not sure there is so much debate, really. Recursive make has some pretty well known limitations. Non-recursive make has different, largely complementary, limitations.

That being understood, I'm still trying to get one to work.

Lots of people do. But although you may understand that recursive make has known issues, you do not seem to understand their nature, because you are asking about a manifestation of one of main ones.

Problem: The problem I have is that when I run the makefile at the root level again, it will not pick up if there have been changes to either the .c or .h files in the subdirectory.

No, it doesn't. That is to be expected with your makefile.

Recursive make serves large projects by dividing build information into more manageable pieces and keeping it close to the sources being built. Among the main costs of doing so is that details, especially dependency details, are compartmentalized. In your case, the top-level make knows that a target src/zmachine/zmachine.a is to be built, but no dependencies for that target are known to it. As a result, that make considers the target out of date only if it does not exist. So yes, it will not recognize that target as being out of date relative to its actual sources. That a sub-make would update it if run is irrelevant, because the sub-make never runs.

The usual, more practicable approach to recursive make is to recurse unconditionally. Something like this:

The way make works is, if you don't provide an argument, it will start by scanning the Makefile looking for the "default goal". The default goal is simply the first target it encounters (notice it's the first target, not targets).

In your case, the rule: