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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package poll supports non-blocking I/O on file descriptors with polling.
// This supports I/O operations that block only a goroutine, not a thread.
// This is used by the net and os packages.
// It uses a poller built into the runtime, with support from the
// runtime scheduler.
package poll
import (
// ErrNetClosing is returned when a network descriptor is used after
// it has been closed. Keep this string consistent because of issue
// #4373: since historically programs have not been able to detect
// this error, they look for the string.
var ErrNetClosing = errors.New("use of closed network connection")
// ErrFileClosing is returned when a file descriptor is used after it
// has been closed.
var ErrFileClosing = errors.New("use of closed file")
// ErrNoDeadline is returned when a request is made to set a deadline
// on a file type that does not use the poller.
var ErrNoDeadline = errors.New("file type does not support deadline")
// Return the appropriate closing error based on isFile.
func errClosing(isFile bool) error {
if isFile {
return ErrFileClosing
return ErrNetClosing
// ErrDeadlineExceeded is returned for an expired deadline.
// This is exported by the os package as os.ErrDeadlineExceeded.
var ErrDeadlineExceeded error = &DeadlineExceededError{}
// DeadlineExceededError is returned for an expired deadline.
type DeadlineExceededError struct{}
// Implement the net.Error interface.
// The string is "i/o timeout" because that is what was returned
// by earlier Go versions. Changing it may break programs that
// match on error strings.
func (e *DeadlineExceededError) Error() string { return "i/o timeout" }
func (e *DeadlineExceededError) Timeout() bool { return true }
func (e *DeadlineExceededError) Temporary() bool { return true }
// ErrNotPollable is returned when the file or socket is not suitable
// for event notification.
var ErrNotPollable = errors.New("not pollable")
// consume removes data from a slice of byte slices, for writev.
func consume(v *[][]byte, n int64) {
for len(*v) > 0 {
ln0 := int64(len((*v)[0]))
if ln0 > n {
(*v)[0] = (*v)[0][n:]
n -= ln0
*v = (*v)[1:]
// TestHookDidWritev is a hook for testing writev.
var TestHookDidWritev = func(wrote int) {}