mmap.go RawHistoryFolder

1package hints
2
3import "syscall"
4
5// mapping is a byte region that lives outside the Go heap: anonymous memory
6// from mmap, returned to the system by unmap. When mmap fails it falls back
7// to heap memory, which unmap then just drops.
8type mapping struct {
9	b      []byte
10	mapped bool
11	live   *int
12}
13
14// alloc returns a zeroed region of n bytes; w.live counts the regions not
15// yet released.
16func (w *worker) alloc(n int) *mapping {
17	m := &mapping{live: &w.live}
18	b, err := syscall.Mmap(-1, 0, n, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANON)
19	if err != nil {
20		b = make([]byte, n)
21	} else {
22		m.mapped = true
23	}
24	m.b = b
25	w.live++
26	return m
27}
28
29// unmap releases the region; it is safe to call twice and on nil. The
30// region must not be used afterwards, nor still be written by the output.
31func (m *mapping) unmap() {
32	if m == nil || m.b == nil {
33		return
34	}
35	if m.mapped {
36		_ = syscall.Munmap(m.b)
37	}
38	m.b = nil
39	*m.live--
40}