Refactor loop code into its own package

tools/utils/select.go

@@ -0,0 +1,103 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+type Selector struct {
+	read_set, write_set, err_set unix.FdSet
+	read_fds, write_fds, err_fds map[int]bool
+}
+
+func CreateSelect(expected_number_of_fds int) *Selector {
+	var ans Selector
+	ans.read_fds = make(map[int]bool, expected_number_of_fds)
+	ans.write_fds = make(map[int]bool, expected_number_of_fds)
+	ans.err_fds = make(map[int]bool, expected_number_of_fds)
+	return &ans
+}
+
+func (self *Selector) register(fd int, fdset *map[int]bool) {
+	(*fdset)[fd] = true
+}
+
+func (self *Selector) RegisterRead(fd int) {
+	self.register(fd, &self.read_fds)
+}
+
+func (self *Selector) RegisterWrite(fd int) {
+	self.register(fd, &self.write_fds)
+}
+
+func (self *Selector) RegisterError(fd int) {
+	self.register(fd, &self.err_fds)
+}
+
+func (self *Selector) unregister(fd int, fdset *map[int]bool) {
+	(*fdset)[fd] = false
+}
+
+func (self *Selector) UnRegisterRead(fd int) {
+	self.unregister(fd, &self.read_fds)
+}
+
+func (self *Selector) UnRegisterWrite(fd int) {
+	self.unregister(fd, &self.write_fds)
+}
+
+func (self *Selector) UnRegisterError(fd int) {
+	self.unregister(fd, &self.err_fds)
+}
+
+func (self *Selector) Wait(timeout time.Duration) (num_ready int, err error) {
+	self.read_set.Zero()
+	self.write_set.Zero()
+	self.err_set.Zero()
+	max_fd_num := 0
+
+	init_set := func(s *unix.FdSet, m *map[int]bool) {
+		s.Zero()
+		for fd, enabled := range *m {
+			if fd > -1 && enabled {
+				if max_fd_num < fd {
+					max_fd_num = fd
+				}
+				s.Set(fd)
+			}
+		}
+	}
+	init_set(&self.read_set, &self.read_fds)
+	init_set(&self.write_set, &self.write_fds)
+	init_set(&self.err_set, &self.err_fds)
+	num_ready, err = Select(max_fd_num+1, &self.read_set, &self.write_set, &self.err_set, timeout)
+	if err == unix.EINTR {
+		return 0, nil
+	}
+	return
+}
+
+func (self *Selector) WaitForever() (num_ready int, err error) {
+	return self.Wait(-1)
+}
+
+func (self *Selector) IsReadyToRead(fd int) bool {
+	return fd > -1 && self.read_set.IsSet(fd)
+}
+
+func (self *Selector) IsReadyToWrite(fd int) bool {
+	return fd > -1 && self.write_set.IsSet(fd)
+}
+
+func (self *Selector) IsErrored(fd int) bool {
+	return fd > -1 && self.err_set.IsSet(fd)
+}
+
+func (self *Selector) UnregisterAll() {
+	self.read_fds = make(map[int]bool)
+	self.write_fds = make(map[int]bool)
+	self.err_fds = make(map[int]bool)
+}