1/* 2 Copyright The containerd Authors. 3 4 Licensed under the Apache License, Version 2.0 (the "License"); 5 you may not use this file except in compliance with the License. 6 You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10 Unless required by applicable law or agreed to in writing, software 11 distributed under the License is distributed on an "AS IS" BASIS, 12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 See the License for the specific language governing permissions and 14 limitations under the License. 15*/ 16 17package ioutil 18 19import ( 20 "errors" 21 "io" 22 "sync" 23) 24 25// WriterGroup is a group of writers. Writer could be dynamically 26// added and removed. 27type WriterGroup struct { 28 mu sync.Mutex 29 writers map[string]io.WriteCloser 30 closed bool 31} 32 33var _ io.Writer = &WriterGroup{} 34 35// NewWriterGroup creates an empty writer group. 36func NewWriterGroup() *WriterGroup { 37 return &WriterGroup{ 38 writers: make(map[string]io.WriteCloser), 39 } 40} 41 42// Add adds a writer into the group. The writer will be closed 43// if the writer group is closed. 44func (g *WriterGroup) Add(key string, w io.WriteCloser) { 45 g.mu.Lock() 46 defer g.mu.Unlock() 47 if g.closed { 48 w.Close() 49 return 50 } 51 g.writers[key] = w 52} 53 54// Get gets a writer from the group, returns nil if the writer 55// doesn't exist. 56func (g *WriterGroup) Get(key string) io.WriteCloser { 57 g.mu.Lock() 58 defer g.mu.Unlock() 59 return g.writers[key] 60} 61 62// Remove removes a writer from the group. 63func (g *WriterGroup) Remove(key string) { 64 g.mu.Lock() 65 defer g.mu.Unlock() 66 w, ok := g.writers[key] 67 if !ok { 68 return 69 } 70 w.Close() 71 delete(g.writers, key) 72} 73 74// Write writes data into each writer. If a writer returns error, 75// it will be closed and removed from the writer group. It returns 76// error if writer group is empty. 77func (g *WriterGroup) Write(p []byte) (int, error) { 78 g.mu.Lock() 79 defer g.mu.Unlock() 80 for k, w := range g.writers { 81 n, err := w.Write(p) 82 if err == nil && len(p) == n { 83 continue 84 } 85 // The writer is closed or in bad state, remove it. 86 w.Close() 87 delete(g.writers, k) 88 } 89 if len(g.writers) == 0 { 90 return 0, errors.New("writer group is empty") 91 } 92 return len(p), nil 93} 94 95// Close closes the writer group. Write will return error after 96// closed. 97func (g *WriterGroup) Close() { 98 g.mu.Lock() 99 defer g.mu.Unlock() 100 for _, w := range g.writers { 101 w.Close() 102 } 103 g.writers = nil 104 g.closed = true 105} 106