M:N threading

[andrewrk]

• add std.atomic.QueueMpsc.isEmpty
• make std.debug.global_allocator thread-safe
• std.event.Loop: now you have to choose between
  • initSingleThreaded
  • initMultiThreaded
• std.event.Loop multiplexes coroutines onto kernel threads
• Remove std.event.Loop.stop. Instead the event loop run() function
  returns once there are no pending coroutines.
• fix crash in ir.cpp for calling methods under some conditions
• small progress self-hosted compiler, analyzing top level declarations
• Introduce std.event.Lock for synchronizing coroutines
• introduce std.event.Locked(T) for data that only 1 coroutine should
  modify at once.
• make the self hosted compiler use multi threaded event loop
• make std.heap.DirectAllocator thread-safe

See #174

TODO:

• call sched_getaffinity instead of hard coding thread pool size 4
• support for Windows
• support for MacOS
• provide guarantees about whether memory goes in the coroutine frame or stack frame #1194
• ability to "bundle" more errors before the first suspend point in an async function #1197

[kristate]

Wondering if we need an abstraction for FDs;
On windows we have to work with typedef void * HANDLE

Better to get threading out of the way first before we fine tune event loops, though.

[kristate]

Also, this might be of curiosity to you:
https://blog.marcgravell.com/2018/07/pipe-dreams-part-1.html

[andrewrk]

Got it working on MacOS, next up Windows

[andrewrk]

@bnoordhuis looks like libuv uses IO Completion Ports. Do you recommend this approach?

[andrewrk]

nevermind, it's already done. that was a surprisingly nice API.