runtime error regardless of stack size in spawn_stack

[ghost]

This program triggers runtime error regardless of StackSize (16kB is lowest possible on pthreads):
https://gist.github.com/8533006

"fatal runtime error: assertion failed: !ptr.is_null()" + easter egg

I tried with stack sizes from 16kB up to 128MB, and all fail in same assertion.

When I replace "std::rt::thread::Thread::spawn_stack(StackSize)" with "spawn" runtime error is not triggered.

[Aatch]

Are you replacing std::rt::thread::Thread::spawn_stack with std::rt::thread::Thread::spawn or just a call to spawn? Since Thread::spawn is implemented in terms of Thread::spawn_stack, I would expect the error to be present for both.

[ghost]

I replace std::rt::thread::Thread::spawn_stack(StackSize) with just a call to spawn without Thread:: prefix.

[alexcrichton]

This is because we implement a "red zone" of stack at then end of a green thread's stack, and the red zone has size 20K. The thread is considered to have overflowed its stack once it enters the red zone. Obviously it's bad that the entire stack is considered the red zone.

I'm nominating this because I think this warrants discussion about what to do in this situation. The red zone allows rust_stack_exhausted to run as well as run any user-defined dtors near the end of the stack. If you specify a stack size that's less than the RED_ZONE size, then should you abort when you overflow the stack unconditionally? Should the red zone just be smaller?

Decisions, decisions...

[pnkfelix]

our documentation regarding minimum stack sizes and the relationship of requested stack size versus the actual allocated stack size may need some help.

But more importantly, the bug described here does not quite match up with the diagnosis acrichto provided. Need to do a little more investigation.

Not accepting for milestone for now.

[pnkfelix]

assigning P-low.

[alexcrichton]

This was fixed by b02b5cd, and has tests checked in.

The original code in the gist actually failed for reasons unrelated to stack size. When attempting to block on a channel, a local task is required (and none was found), triggering the assertion.