Hacker News Reader

Comment by tombert | Hacker News Reader

I had a friend who worked for one of the big Market Makers, and he told me that they would indeed turn the GC off, but what they'd do is just pre-allocate everything into bigass arrays before-hand, and have incrementers to simulate the "new" keyword. They might do this in something more or less like a threadlocal to avoid having to deal with locks or race conditions or anything like that.

View on HN

This is called bump or arena allocation, depending on how you want to define it.

Sometimes also referred to as Object pools.

A lot of game engines do this, avoiding the cost of a malloc lookup by just allocating everything as a stack

Seen some audio engines that do this too. You can come up with an elegant non-blocking lock free allocator and pass updates from the user thread out to system and reserve the memory, or you can just up front allocate everything that's needed.

If it's a fixed function synth, sometimes just allocating everything up front makes more sense.

Kernel drivers, too. Especially the DMA buffers for devices that don’t support scatter gather: if you don’t allocate them at driver startup, you might not be able to find enough free contiguous regions later. Although maybe that’s not as big of a deal these days, since both Windows and Linux can relocate physical pages.

I remember seeing a Java game engine that included a container that you were supposed to dump unused objects into to prevent GC from running in the middle of a level. At the end of the level, you could empty the container, and let the GC run during the loading screen or whatever.

It was a deliberate design choice that was surprisingly close to what the original article describes.

This is like going back to malloc and free but using array indices rather than pointers, and each type has a fixed-size heap. We did it in one Microsoft service because the very first .NET releases had slow GCs.

One could argue that pointers are just array indices, where the array is your whole address space, and you only get the one array for all your types.

It helps that pointer-to-T is a distinct type, where (apart from Ada) index-into-array-of-T is just like any other integer.

Standard approach in systems for critical applications like aerospace: https://www.quora.com/How-does-SpaceX-handle-memory-manageme...

Reply on news.ycombinator.com