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Implement parallelism patterns
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Tamer Tas
parent
4c276c72e1
commit
4f4ceb2dc1
121
bounded_parallelism/md5.go
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121
bounded_parallelism/md5.go
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@ -0,0 +1,121 @@
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package bounded_parallelism
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import (
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"crypto/md5"
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"errors"
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"fmt"
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"io/ioutil"
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"os"
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"path/filepath"
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"sort"
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"sync"
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)
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// walkFiles starts a goroutine to walk the directory tree at root and send the
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// path of each regular file on the string channel. It sends the result of the
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// walk on the error channel. If done is closed, walkFiles abandons its work.
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func walkFiles(done <-chan struct{}, root string) (<-chan string, <-chan error) {
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paths := make(chan string)
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errc := make(chan error, 1)
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go func() { // HL
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// Close the paths channel after Walk returns.
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defer close(paths) // HL
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// No select needed for this send, since errc is buffered.
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errc <- filepath.Walk(root, func(path string, info os.FileInfo, err error) error { // HL
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if err != nil {
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return err
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}
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if !info.Mode().IsRegular() {
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return nil
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}
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select {
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case paths <- path: // HL
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case <-done: // HL
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return errors.New("walk canceled")
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}
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return nil
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})
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}()
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return paths, errc
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}
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// A result is the product of reading and summing a file using MD5.
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type result struct {
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path string
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sum [md5.Size]byte
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err error
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}
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// digester reads path names from paths and sends digests of the corresponding
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// files on c until either paths or done is closed.
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func digester(done <-chan struct{}, paths <-chan string, c chan<- result) {
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for path := range paths { // HLpaths
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data, err := ioutil.ReadFile(path)
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select {
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case c <- result{path, md5.Sum(data), err}:
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case <-done:
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return
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}
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}
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}
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// MD5All reads all the files in the file tree rooted at root and returns a map
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// from file path to the MD5 sum of the file's contents. If the directory walk
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// fails or any read operation fails, MD5All returns an error. In that case,
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// MD5All does not wait for inflight read operations to complete.
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func MD5All(root string) (map[string][md5.Size]byte, error) {
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// MD5All closes the done channel when it returns; it may do so before
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// receiving all the values from c and errc.
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done := make(chan struct{})
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defer close(done)
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paths, errc := walkFiles(done, root)
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// Start a fixed number of goroutines to read and digest files.
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c := make(chan result) // HLc
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var wg sync.WaitGroup
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const numDigesters = 20
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wg.Add(numDigesters)
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for i := 0; i < numDigesters; i++ {
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go func() {
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digester(done, paths, c) // HLc
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wg.Done()
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}()
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}
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go func() {
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wg.Wait()
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close(c) // HLc
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}()
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// End of pipeline. OMIT
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m := make(map[string][md5.Size]byte)
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for r := range c {
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if r.err != nil {
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return nil, r.err
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}
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m[r.path] = r.sum
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}
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// Check whether the Walk failed.
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if err := <-errc; err != nil { // HLerrc
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return nil, err
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}
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return m, nil
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}
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func main() {
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// Calculate the MD5 sum of all files under the specified directory,
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// then print the results sorted by path name.
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m, err := MD5All(os.Args[1])
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if err != nil {
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fmt.Println(err)
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return
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}
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var paths []string
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for path := range m {
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paths = append(paths, path)
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}
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sort.Strings(paths)
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for _, path := range paths {
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fmt.Printf("%x %s\n", m[path], path)
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}
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}
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109
parallelism/md5.go
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109
parallelism/md5.go
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@ -0,0 +1,109 @@
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package parallelism
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import (
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"crypto/md5"
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"errors"
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"fmt"
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"io/ioutil"
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"os"
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"path/filepath"
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"sort"
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"sync"
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)
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// A result is the product of reading and summing a file using MD5.
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type result struct {
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path string
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sum [md5.Size]byte
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err error
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}
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// sumFiles starts goroutines to walk the directory tree at root and digest each
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// regular file. These goroutines send the results of the digests on the result
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// channel and send the result of the walk on the error channel. If done is
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// closed, sumFiles abandons its work.
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func sumFiles(done <-chan struct{}, root string) (<-chan result, <-chan error) {
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// For each regular file, start a goroutine that sums the file and sends
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// the result on c. Send the result of the walk on errc.
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c := make(chan result)
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errc := make(chan error, 1)
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go func() { // HL
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var wg sync.WaitGroup
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err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
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if err != nil {
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return err
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}
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if !info.Mode().IsRegular() {
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return nil
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}
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wg.Add(1)
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go func() { // HL
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data, err := ioutil.ReadFile(path)
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select {
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case c <- result{path, md5.Sum(data), err}: // HL
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case <-done: // HL
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}
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wg.Done()
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}()
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// Abort the walk if done is closed.
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select {
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case <-done: // HL
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return errors.New("walk canceled")
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default:
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return nil
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}
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})
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// Walk has returned, so all calls to wg.Add are done. Start a
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// goroutine to close c once all the sends are done.
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go func() { // HL
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wg.Wait()
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close(c) // HL
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}()
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// No select needed here, since errc is buffered.
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errc <- err // HL
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}()
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return c, errc
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}
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// MD5All reads all the files in the file tree rooted at root and returns a map
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// from file path to the MD5 sum of the file's contents. If the directory walk
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// fails or any read operation fails, MD5All returns an error. In that case,
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// MD5All does not wait for inflight read operations to complete.
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func MD5All(root string) (map[string][md5.Size]byte, error) {
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// MD5All closes the done channel when it returns; it may do so before
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// receiving all the values from c and errc.
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done := make(chan struct{}) // HLdone
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defer close(done) // HLdone
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c, errc := sumFiles(done, root) // HLdone
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m := make(map[string][md5.Size]byte)
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for r := range c { // HLrange
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if r.err != nil {
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return nil, r.err
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}
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m[r.path] = r.sum
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}
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if err := <-errc; err != nil {
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return nil, err
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}
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return m, nil
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}
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func main() {
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// Calculate the MD5 sum of all files under the specified directory,
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// then print the results sorted by path name.
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m, err := MD5All(os.Args[1])
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if err != nil {
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fmt.Println(err)
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return
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}
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var paths []string
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for path := range m {
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paths = append(paths, path)
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}
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sort.Strings(paths)
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for _, path := range paths {
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fmt.Printf("%x %s\n", m[path], path)
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}
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}
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