perf: reduce `mux` sturct size by merging slices

[rueian]

Currently, a mux struct contains the following 3 slices:

rueidis/mux.go

Lines 93 to 96 in fc56243

	m := &mux{dst: dst, init: init, dead: dead, wireFn: wireFn,
	wire: make([]atomic.Value, multiplex),
	mu: make([]sync.Mutex, multiplex),
	sc: make([]*singleconnect, multiplex),

They take 24*3 bytes per mux. We should merge them into one to save the struct size.

[arbhalerao]

Hi @rueian , I would like to work on this. Please assign it to me, thanks!

[arbhalerao]

Replace the 3 slices with a single slice of structs:

type connection struct {
    wire atomic.Value
    sc   *singleconnect
    mu   sync.Mutex
}

type mux struct {
    // ... existing fields ...

    conns []connection  // replaces wire, sc, mu slices

    // ... existing fields ...
}

Migration:

m.wire[i] → m.conns[i].wire
m.sc[i] → m.conns[i].sc
m.mu[i] → m.conns[i].mu

Or

add helper methods
func (m *mux) getWire(i int) *atomic.Value { return &m.conns[i].wire }
func (m *mux) getSC(i int) **singleconnect { return &m.conns[i].sc }
func (m *mux) getMu(i int) *sync.Mutex { return &m.conns[i].mu }

Constructor change (newMux):

current

wire: make([]atomic.Value, multiplex),
mu:   make([]sync.Mutex, multiplex), 
sc:   make([]*singleconnect, multiplex),

proposed

conns: make([]connection, multiplex),

@rueian If this approach looks good to you, please let me know and I’ll proceed with a PR.

[rueian]

Hi @arbhalerao,

LGTM except for the connection naming. I think connection is too general. I prefer something like muxwire, and helper methods are not necessary.