ScriptReference/Unity.Collections.Allocator.Temp

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ScriptReference/Unity.Collections.Allocator.Temp

https://docs.unity3d.com/ScriptReference/Unity.Collections.Allocator.Temp.html

[vertxxyz]

Allocator.Temp has the fastest allocation. Use it for allocations with a lifespan of one frame or fewer. However, you can’t use Temp to pass NativeContainer allocations to jobs.
(See NativeContainer.)

[vertxxyz]

From kevinmv on the Unity Discord:
Allocator.Temp is indeed thread local.
The allocation is not stack based, as of 2022.1 it uses a bump allocator that is reset based on the current scope. Most temp allocations are reset on the next player update. For jobs, you can allocate using temp inside your Execute as we provide a new temp scope for allocations that live only for the scope of the Execute method itself. And indeed, since temp allocations are thread local, we fail scheduling any native containers [passed into a job] that use Allocator.Temp as you are almost certainly guaranteed to have problems if you refer to temp memory from another thread.
Using Allocator.Temp inside Execute is encouraged if you really need to allocate (best to avoid allocations inside a job when possible but I understand that isn't always the case). The temp allocation will be quite quick since it usually amounts to a pointer addition rather than fetching a new block of memory from the heap.
And since it is thread local, there is no contention on such an allocation unlike TempJob which can be quite slow but provides different lifetime guarantees (4 frames for the alloc before we tell you you likely forgot to free your allocation).