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Add some concepts related to exit(3) #17

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Jan 19, 2023
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Add some concepts related to exit(3) #17

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2b7fb32
Add some concepts related to exit(3)
yamt Dec 15, 2022
ccc5811
Rename thread group to process
yamt Dec 16, 2022
ec8172d
Remove thread_exit for now
yamt Jan 4, 2023
dc1ac30
try to make a sentence less odd
yamt Jan 6, 2023
f74d69d
english improvements
yamt Jan 11, 2023
c732034
english improvement
yamt Jan 11, 2023
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39 changes: 39 additions & 0 deletions README.md
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Expand Up @@ -172,6 +172,45 @@ TID is a 32-bit integer to identify threads created with `wasi_thread_spawn`.
For example, it can be used to indicate the main thread, which doesn't
have a TID in the current version of this proposal.

### Process

* A process is a group of threads.

* The main thread starts with a process which only contains
the main thread.

* Threads created by a thread in a process using `wasi_thread_spawn`
are added to the process.

* When a thread is terminated, it's removed from the process.

### Voluntary thread termination

A thread can terminate itself voluntarily by returning from
`wasi_thread_start`.

### Changes to WASI `proc_exit`

With this proposal, the `proc_exit` function takes extra responsibility
to terminate all threads in the process, not only the calling one.
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How about simply "When proc_exit is called the entire process is terminated, including all running threads". I'm not we need the "takes extra responsibility" wording.

It seems fairly clear from its name that proc_exit would do this, so I don't really see it as "extra responsibility", but maybe thats just my reading of it.

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without wasi-threads, a runtime would simply terminate the calling thread.

when adding wasi-threads support to a runtime, you need to make it terminate other thread too. it would need a significant implementation effort. i feel it's appropriate to call it extra.

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Sure. But don't think that is clear enough to simply say: "When proc_exit is called the entire process is terminated, including all running threads".

(BTW, the way I see it proc_exit brings down the entire process (that is that the proc part means), even without wasi-threads. It just happens that there was only ever one thread previously.)

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maybe. i wanted to somehow emphasize that this is something a runtime needs to implement.


Any of the threads in the process can call `proc_exit`.

### Traps

When a trap occurs in any thread, the entire process is terminated.

### Process exit status

If one or more threads call WASI `proc_exit` or raise a trap,
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Does it include calling it proc_exit from the main thread?

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Yes

one of them is chosen by the runtime to represent the exit status
of the process.
It's non deterministic which one is chosen.

If all the threads in the process have been terminated without calling
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How about, "If that last running thread in a process terminates without calling proc_exit or trapping it is treated as if ... "

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it's not only about the last running thread.

consider a process with two threads.

  1. a thread terminated itself by calling proc_exit(50)
  2. another thread, which is the last running thread, terminates itself by returning from wasi_thread_spawn before the runtime terminates it for proc_exit.
  3. the exit code of the process should be 50.

i think your wording can be interpreted as the exit code of the process can be 0.

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My my understanding, in your example above proc_exit(50) causes all threads to be terminated, so its not possible (2) to occor.

Another way of putting it "proc_exitdoes not complete until all threads are terminated, so not thread can exist afterproc_exit` is complete.

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My my understanding, in your example above proc_exit(50) causes all threads to be terminated, so its not possible (2) to occor.

if things work in a lockstep, maybe.
but we are talking about threads...

Another way of putting it "proc_exitdoes not complete until all threads are terminated, so not thread can exist afterproc_exit` is complete.

in that case, i guess you need to say the thread which called proc_exit is terminated after all other threads are terminated. i feel it's more complicated than the current sentence.

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@sbc100 sbc100 Jan 11, 2023 •
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I think it would odd if we allowed any threads to outlive the thread that calls proc_exit.. the whole point of that system call is to bring down all the threads so logically nothing else can happen on any thread once that syscall completes.

I don't want to hold up this PR, even though I don't love the way this sentence is phrased. I guess we can land this as it stands and try to improve it later.

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Yeah, let me know if #27 addresses some of the things you bring up here...

`proc_exit` or raising a trap, it's treated as if the last thread called
`proc_exit` with exit code 0.
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Should we not mention proc_exit here and just say that exit code is 0? It might get a bit confusing if e.g. in the future proc_exit is extended with additional functionality - in that case, this sentence can be interpreted as that additional functionality should also be executed along with returning 0 as exit code (whereas I think it shouldn't).

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i can't imagine any functionalities which proc_exit might gain but on the other hand should not be a part of this. do you have examples?

even if we avoid mentioning proc_exit here, when you are adding an extra functionality to proc_exit, you still need to consider if the change should apply to this sentence or not.

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@loganek loganek Jan 9, 2023 •
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do you have examples?

No, it was only hypothetical question.

you still need to consider if the change should apply to this sentence or not.

Yes


#### Design choice: pthreads

One of the goals of this API is to be able to support `pthreads` for C compiled
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