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I would like to provide individual names to the threads in my Rust program. These names should appear in top/htop so I can differentiate the thread's job. In Ruby I would modify the argv[0] entry, or maybe Process.setproctitle("foo"). My inspiration is from Ruby's Unicorn web server.

The env::args function returns an Args value. The Args value wraps the platform-specific std::sys::args::args() function which is not reexported for general use. ArgsOs doesn't have a usable mutator (so yes, the stdlib makes it clear it is immutable).

How do I mutate the arguments some other way? I am happy with a Linux-only solution since that is where the real work will happen. Solutions outside the stdlib are also fine.

What path should I take in order to modify the first argument in the environment of my process?

Shepmaster
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xrl
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    *how my Rust program appears* ... *what all my threads are doing* — which is it? Do you care about the program as a whole or specific threads? – Shepmaster Jan 10 '18 at 18:08
  • *In Ruby I would modify the `argv[0]` entry* — did you mean `ARGV`? I wasn't aware that this would change anything outside of the process. Searching for this functionality seems to be difficult, do you have any links so I can learn more about that functionality of Ruby? – Shepmaster Jan 10 '18 at 18:12
  • (just realized that my link was wrong), A thread is NOT a process, why not use name when building the thread ? https://doc.rust-lang.org/std/thread/struct.Builder.html#method.name – Stargateur Jan 10 '18 at 18:25

2 Answers2

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How can I replace an entry in std::env:args()

You cannot. Immutable means immutable.

I would like to change how my Rust program appears in top/htop

There is nothing like this in the standard library. As far as I know, there's no cross-platform solution, so it would be a hard fight to put in there.

Linux

Seems to have a simple enough solution: Change process name without changing argv[0] in Linux

If you only care about Linux, you can use the prctl crate:

prctl::set_name("new_process")

macOS

Has various concepts of "process name" and the solution is complex and uses undocumented / hidden APIs: Setting process name on Mac OS X at runtime

Everything in that answer could be written in Rust using the appropriate bindings to the macOS APIs.

Windows

Does not seem to have such a concept: Changing a process name in runtime

Cross-Platform

Someone could write a crate that abstracts across these different mechanisms, but I'm not aware of one.

so I can easily spot what all my threads are doing

As mentioned in the comments, when you create a thread, you can give it a name. Some work was recently put into renaming threads at run time, but that work stalled out.

Shepmaster
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I wrote the proctitle crate for setting process titles in a cross-platform manner. On Linux it does happen to name the current thread, but this is a quirk of the APIs it provides rather than a deliberate choice.

Thomas Hurst
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