chore: example read-write intensive to memfd file

examples/read-write-memfd/main.go

@@ -0,0 +1,127 @@
+package main
+
+import (
+	"fmt"
+	"reflect"
+	"runtime"
+	"syscall"
+	"time"
+	"unsafe"
+
+	uring "github.com/ii64/gouring"
+	"golang.org/x/sys/unix"
+)
+
+func main() {
+	ring, err := uring.New(64, 0)
+	if err != nil {
+		panic(err)
+	}
+	defer ring.Close()
+
+	fd, err := unix.MemfdCreate("mymemfd", unix.MFD_CLOEXEC)
+	if err != nil {
+		panic(err)
+	}
+	defer unix.Close(fd)
+
+	const BSIZE = 512
+	unix.Ftruncate(fd, BSIZE)
+
+	addr, err := mmap(nil, BSIZE, syscall.PROT_READ|syscall.PROT_WRITE|syscall.PROT_EXEC, syscall.MAP_SHARED, fd, 0)
+	if err != nil {
+		panic(err)
+	}
+	defer munmap(addr, BSIZE)
+
+	var rbuf []byte
+	sh := (*reflect.SliceHeader)(unsafe.Pointer(&rbuf))
+	sh.Data = uintptr(addr)
+	sh.Cap = BSIZE
+	sh.Len = BSIZE
+
+	tnow := func() string { return fmt.Sprintf("CLOCK:%d\n", time.Now().UnixMilli()) }
+
+	go func() {
+		flen := len(tnow())
+		// monitor written bytes
+		for {
+			// copy
+			payload := string(rbuf[:flen])
+			fmt.Printf("> %q\n", payload)
+			time.Sleep(time.Millisecond * 50)
+		}
+	}()
+
+	var buf [BSIZE]byte
+	refresh := func() int {
+		b := []byte(tnow())
+		copy(buf[:], b)
+		return len(b)
+	}
+
+	qWrite := func() {
+		sqe := ring.GetSqe()
+		uring.PrepWrite(sqe, fd, &buf[0], refresh(), 0)
+		sqe.UserData.SetUint64(0xaaaaaaaa)
+	}
+	qRead := func() {
+		sqe := ring.GetSqe()
+		uring.PrepRead(sqe, fd, &buf[0], len(buf), 0)
+		sqe.UserData.SetUint64(0xbbbbbbbb)
+	}
+
+	qWrite()
+
+	submitted, err := ring.SubmitAndWait(1)
+	if err != nil {
+		panic(err)
+	}
+	println("submitted:", submitted)
+
+	var cqe *uring.IoUringCqe
+	for {
+		err = ring.WaitCqe(&cqe)
+		switch err {
+		case syscall.EINTR, syscall.EAGAIN, syscall.ETIME:
+			runtime.Gosched()
+			continue
+		case nil:
+			goto cont
+		default:
+			panic(err)
+		}
+	cont:
+		switch cqe.UserData {
+		case 0xaaaaaaaa:
+			qRead()
+		case 0xbbbbbbbb:
+			qWrite()
+		}
+
+		ring.SeenCqe(cqe)
+		submitted, err := ring.Submit()
+		if err != nil {
+			panic(err)
+		} else {
+			_ = submitted
+			// println("submitted:", submitted)
+		}
+	}
+
+}
+
+//go:linkname mmap syscall.mmap
+func mmap(addr unsafe.Pointer, length uintptr, prot int, flags int, fd int, offset int64) (xaddr unsafe.Pointer, err error)
+
+//go:linkname munmap syscall.munmap
+func munmap(addr unsafe.Pointer, length uintptr) (err error)
+
+func msync(addr unsafe.Pointer, length uintptr, flags uintptr) error {
+	r1, _, e1 := syscall.Syscall(syscall.SYS_MSYNC, uintptr(addr), length, flags)
+	if e1 != 0 {
+		return syscall.Errno(e1)
+	}
+	_ = r1
+	return nil
+}