1 files changed, 41 insertions, 0 deletions
diff --git a/src/runtime/internal/sys/nih.go b/src/runtime/internal/sys/nih.go
new file mode 100644
index 0000000..17eab67
--- /dev/null
+++ b/src/runtime/internal/sys/nih.go
@@ -0,0 +1,41 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sys
+
+// NOTE: keep in sync with cmd/compile/internal/types.CalcSize
+// to make the compiler recognize this as an intrinsic type.
+type nih struct{}
+
+// NotInHeap is a type must never be allocated from the GC'd heap or on the stack,
+// and is called not-in-heap.
+//
+// Other types can embed NotInHeap to make it not-in-heap. Specifically, pointers
+// to these types must always fail the `runtime.inheap` check. The type may be used
+// for global variables, or for objects in unmanaged memory (e.g., allocated with
+// `sysAlloc`, `persistentalloc`, r`fixalloc`, or from a manually-managed span).
+//
+// Specifically:
+//
+// 1. `new(T)`, `make([]T)`, `append([]T, ...)` and implicit heap
+// allocation of T are disallowed. (Though implicit allocations are
+// disallowed in the runtime anyway.)
+//
+// 2. A pointer to a regular type (other than `unsafe.Pointer`) cannot be
+// converted to a pointer to a not-in-heap type, even if they have the
+// same underlying type.
+//
+// 3. Any type that containing a not-in-heap type is itself considered as not-in-heap.
+//
+// - Structs and arrays are not-in-heap if their elements are not-in-heap.
+// - Maps and channels contains no-in-heap types are disallowed.
+//
+// 4. Write barriers on pointers to not-in-heap types can be omitted.
+//
+// The last point is the real benefit of NotInHeap. The runtime uses
+// it for low-level internal structures to avoid memory barriers in the
+// scheduler and the memory allocator where they are illegal or simply
+// inefficient. This mechanism is reasonably safe and does not compromise
+// the readability of the runtime.
+type NotInHeap struct{ _ nih }