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September 17, 2023 15:02
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ringbuffer
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package ringbuffer_safe | |
import ( | |
"log" | |
"os" | |
"os/signal" | |
"runtime" | |
"sync/atomic" | |
"time" | |
) | |
const free = int32(0) // 0 check, state is free, ringbuffer can be accessed | |
const busy = int32(42) // 42 (or any number), state is busy, ringbuffer cannot be accessed | |
// ringbuffer underlying array length | |
const ringBufferLength = 1024 | |
// fixed example entry to read/write | |
const TXT = "help-me!" | |
// entry type of ring buffer | |
type entry struct { | |
prio int | |
data string | |
} | |
func Lock(state *int32) { | |
for !atomic.CompareAndSwapInt32(state, free, busy) { // any other non-zero value, 42 is just an example | |
runtime.Gosched() // poke the scheduler | |
} | |
} | |
func Unlock(state *int32) { | |
atomic.StoreInt32(state, free) // once atomic always atomic | |
} | |
// ring buffer counting the number of rw-operations | |
type RingBuffer struct { | |
writelock *int32 // 0 means free | |
readlock *int32 | |
buffer [ringBufferLength]entry | |
writeIndex int | |
readIndex int | |
counter int | |
} | |
func (r *RingBuffer) read() (b []entry, ok bool) { | |
b = make([]entry, 0, 2) | |
// flag signaling if read value was valid | |
for r.readIndex != r.writeIndex { | |
ok = true | |
b = append(b, r.buffer[r.readIndex]) | |
r.readIndex++ | |
if r.readIndex >= ringBufferLength { | |
r.readIndex %= ringBufferLength | |
} | |
r.counter++ | |
} | |
return b, ok | |
} | |
func (r *RingBuffer) write(b []entry) { | |
for i := range b { | |
if ((r.readIndex - 1) % ringBufferLength) == r.writeIndex { | |
break | |
} | |
r.buffer[r.writeIndex] = b[i] | |
r.writeIndex += 1 | |
if r.writeIndex >= ringBufferLength { | |
r.writeIndex %= ringBufferLength | |
} | |
} | |
} | |
func writeRingBuffer(r *RingBuffer) { | |
for { | |
// only enter here, as long as the writelock value does not equal the free value | |
// once the values are the same, in an atomic operation also set it to busy | |
Lock(r.writelock) | |
r.write([]entry{entry{prio: 1, data: TXT}}) | |
Unlock(r.writelock) | |
} | |
} | |
func readRingBuffer(r *RingBuffer) { | |
for { | |
Lock(r.readlock) | |
r.read() | |
Unlock(r.readlock) | |
} | |
} | |
func NewRingbuffer() *RingBuffer { | |
readlock := int32(0) | |
writelock := int32(0) | |
return &RingBuffer{ | |
writelock: &writelock, | |
readlock: &readlock, | |
} | |
} | |
func Run() int { | |
rb := NewRingbuffer() | |
// simulate external call to write to ringbuffer | |
go writeRingBuffer(rb) | |
// go writeRingBuffer(rb) | |
// go writeRingBuffer(rb) | |
// simulate external call to read from ringbuffer | |
go readRingBuffer(rb) | |
// go readRingBuffer(rb) | |
// go readRingBuffer(rb) | |
// Right way to stop the server using a SHUTDOWN HOOK | |
// Create a channel to receive OS signals | |
c := make(chan os.Signal) | |
// Relay os.Interrupt to our channel (os.Interrupt = CTRL+C) | |
// Ignore other incoming signals | |
signal.Notify(c, os.Interrupt) | |
go func() { | |
time.Sleep(time.Second * 1) | |
c <- os.Interrupt | |
}() | |
// Block main routine until a signal is received | |
// As long as user doesn't press CTRL+C a message | |
// is not passed and our main routine keeps running | |
<-c | |
log.Println("count", rb.counter) | |
return rb.counter | |
} |
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