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syncs: add Map.LoadFunc (#9869)

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The LoadFunc loads a value and calls a user-provided function.
The utility of this method is to ensure that the map lock is held
while executing user-provided logic.
This allows us to solve TOCTOU bugs that would be nearly imposible
to the solve without this API.

Updates tailscale/corp#14772

Signed-off-by: Joe Tsai <joetsai@digital-static.net>
This commit is contained in:
Joe Tsai
2023-10-18 15:02:45 -07:00
committed by GitHub
parent afb72ecd73
commit 674beabc73
2 changed files with 30 additions and 3 deletions
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10
syncs/syncs_test.go
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@ -81,6 +81,11 @@ func TestMap(t *testing.T) {
if v, ok := m.Load("noexist"); v != 0 || ok {
t.Errorf(`Load("noexist") = (%v, %v), want (0, false)`, v, ok)
}
m.LoadFunc("noexist", func(v int, ok bool) {
if v != 0 || ok {
t.Errorf(`LoadFunc("noexist") = (%v, %v), want (0, false)`, v, ok)
}
})
m.Store("one", 1)
if v, ok := m.LoadOrStore("one", -1); v != 1 || !ok {
t.Errorf(`LoadOrStore("one", 1) = (%v, %v), want (1, true)`, v, ok)
@ -88,6 +93,11 @@ func TestMap(t *testing.T) {
if v, ok := m.Load("one"); v != 1 || !ok {
t.Errorf(`Load("one") = (%v, %v), want (1, true)`, v, ok)
}
m.LoadFunc("one", func(v int, ok bool) {
if v != 1 || !ok {
t.Errorf(`LoadFunc("one") = (%v, %v), want (1, true)`, v, ok)
}
})
if v, ok := m.LoadOrStore("two", 2); v != 2 || ok {
t.Errorf(`LoadOrStore("two", 2) = (%v, %v), want (2, false)`, v, ok)
}