Runtime

How Go's reflect Package Reads Types: The rtype and the Method Table

Oct 21, 2026 13 min read Jay Hubbert

reflect reads the runtime’s own abi.Type descriptors; a reflect.Value is a (typ, ptr, flag) triple whose flag word encodes kind, indirection, addressability and read-only state in …

Go Internals Reflection Runtime Performance

range over func: The Compiler Turns a Loop Into a Coroutine

Oct 21, 2026 20 min read Jay Hubbert

The compiler rewrites a range-over-func loop into a yield callback, tracks iterator misbehaviour with a state machine, and hands coroutine switching to iter.Pull.

Go Internals Iterators Compiler Runtime

runtime.AddCleanup: How Go Replaced Finalizers With a Queue of Specials

Oct 21, 2026 19 min read Jay Hubbert

runtime.AddCleanup replaces SetFinalizer with span specials, a lock-free block queue and a pool of cleanup goroutines, so cleanups run promptly and in parallel instead of one at a …

Go Internals Garbage collection Finalizers Runtime

Weak Pointers in Go: The Runtime's Special Span for Non-Tracked Objects

Oct 21, 2026 16 min read Jay Hubbert

weak.Pointer is backed by a per-object special record holding a uintptr handle, which the GC scans as a root but never treats as a strong reference, so the target can still be …

Go Internals Garbage collection Weak pointers Runtime

Why Go Randomizes Map Iteration: The Attack It Prevents

Oct 21, 2026 14 min read Jay Hubbert

Map iteration picks two random offsets at start-up - one in the table directory, one in the slot space - and every map gets a random hash seed, which together defeat hash-flooding …

Go Internals Runtime Maps Security