[BUG] Possibly mssing target dependencies in Makefile

[NexAdn]

Describe the bug

In Gentoo Bug 884005 we noticed builds failing due to files not being created with e.g. this output from the Tinderbox:

Assembler messages:
Fatal error: can't create obj/btop_menu.o: No such file or directory
Assembler messages:
Fatal error: can't create obj/btop_draw.o: No such file or directory

As described by a user on the gentoo-user mailing list, the problem might be that the mkdir commands for the output directories didn't finish before some jobs attempted to open files in said directories, leading to write failures.

To Reproduce

The aforementioned user got this problem by building on a machine with many jobs in parallel (here it was -j17).

Expected behavior

The compiler should be able to open the files for writing.

Screenshots

Screenshots not applicable, but you might be interested in some of this output:

• Tinderbox build log
• First comment on Bug 884005 (contains a condensed output with less noise)
• Environment variables set during build
• emerge --info (contains a bunch of system and package manager information from the build)

Info (please complete the following information):

• btop++ version: btop -v – Not applicable, since the build failed. As can be deduced from the build log, a build of 1.2.13 was attempted.
• Binary: self compiled
• (If compiled) Compiler and version: From the build log: CXX ?| x86_64-pc-linux-gnu-g++ (12.2.1)
• Architecture: [x86_64, aarch64, etc.] uname -m: amd64
• Platform: Gentoo Linux
• (Linux) Kernel: uname -r: Linux-6.0.10-x86_64-AMD_Ryzen_9_5950X_16-Core_Processor-with-glibc2.36
• (OSX/FreeBSD) Os release version: Not applicable
• Terminal used: Not applicable
• Font used: Not applicable

Additional context

contents of ~/.config/btop/btop.log – Not applicable

GDB Backtrace

Not applicable.

[NexAdn]

As we already discussed in the Gentoo bug, the issue is probably that the build targets don't depend on the directories target, thus allowing make to execute both targets in parallel, which breaks the build on the rare occasion that mkdir takes longer than g++ takes to make the open() call.

[NexAdn]

Of course depending on the directories target is not possible for this build system as the dependencies are used as input to the g++ command lines, thus forbidding a dependency on phony targets.

An alternative solution might be calling mkdir -p in the build jobs.
This is an idempotent way of creating the output directories and should be multi-job safe.
Or one could rewrite the all target to call $(MAKE) instead of using the dependcy mechanism:

all:
    $(MAKE) directories
    $(MAKE) btop

[Flowdalic]

I think this is a prime use case for an order-only prerequisite.

[NexAdn]

Didn't even know that existed, but StackOverflow helped 😅

I'll open a PR.