Constant GC allocations when sending large messages to threads?

[Steven Schveighoffer]

On 1/29/20 2:48 PM, cc wrote:
> Given the sample program at https://pastebin.com/u9sSNtj7
> I'm experiencing GC allocations with every call to std.concurrency.send 
> when sending larger messages (e.g. multiple ulongs).  These do not occur 
> when sending uints in comparison, in the provided example.
> 
> For example, when the ManyAllocations version is set, I see results like:
> allocations: 100  bytes: 3280
> 
> When commented out, I see:
> allocations: 1  bytes: 80
> 
> Is there a way to mitigate this memory usage?
> 
> Using DMD32 D Compiler v2.089.1-dirty on Windows 10 x64
> cmdline: rdmd.exe -m64
> 

I'm pretty sure std.concurrency uses Variant to pass message data, which 
boxes when it gets over a certain size. You are probably crossing that 
threshold.

The allocations should level out eventually when the GC starts 
collecting them.

-Steve