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io: reimplement Pipe
No known bugs in the current pipe, but this one is simpler and easier to understand. R=iant CC=golang-dev https://golang.org/cl/4252057
This commit is contained in:
Russ Cox
parent
c7ef0fd26b
commit
6d6f3381ff
@ -9,7 +9,6 @@ package io
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import (
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"os"
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"runtime"
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"sync"
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)
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@ -18,208 +17,114 @@ type pipeResult struct {
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err os.Error
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}
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// Shared pipe structure.
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// A pipe is the shared pipe structure underlying PipeReader and PipeWriter.
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type pipe struct {
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// Reader sends on cr1, receives on cr2.
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// Writer does the same on cw1, cw2.
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r1, w1 chan []byte
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r2, w2 chan pipeResult
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rclose chan os.Error // read close; error to return to writers
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wclose chan os.Error // write close; error to return to readers
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done chan int // read or write half is done
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rl sync.Mutex // gates readers one at a time
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wl sync.Mutex // gates writers one at a time
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l sync.Mutex // protects remaining fields
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data []byte // data remaining in pending write
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rwait sync.Cond // waiting reader
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wwait sync.Cond // waiting writer
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rerr os.Error // if reader closed, error to give writes
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werr os.Error // if writer closed, error to give reads
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}
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func (p *pipe) run() {
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var (
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rb []byte // pending Read
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wb []byte // pending Write
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wn int // amount written so far from wb
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rerr os.Error // if read end is closed, error to send to writers
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werr os.Error // if write end is closed, error to send to readers
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r1 chan []byte // p.cr1 or nil depending on whether Read is ok
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w1 chan []byte // p.cw1 or nil depending on whether Write is ok
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ndone int
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)
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// Read and Write are enabled at the start.
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r1 = p.r1
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w1 = p.w1
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func (p *pipe) read(b []byte) (n int, err os.Error) {
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// One reader at a time.
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p.rl.Lock()
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defer p.rl.Unlock()
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p.l.Lock()
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defer p.l.Unlock()
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for {
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select {
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case <-p.done:
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if ndone++; ndone == 2 {
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// both reader and writer are gone
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// close out any existing i/o
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if r1 == nil {
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p.r2 <- pipeResult{0, os.EINVAL}
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}
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if w1 == nil {
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p.w2 <- pipeResult{0, os.EINVAL}
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}
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return
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}
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continue
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case rerr = <-p.rclose:
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if w1 == nil {
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// finish pending Write
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p.w2 <- pipeResult{wn, rerr}
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wn = 0
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w1 = p.w1 // allow another Write
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}
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if r1 == nil {
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// Close of read side during Read.
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// finish pending Read with os.EINVAL.
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p.r2 <- pipeResult{0, os.EINVAL}
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r1 = p.r1 // allow another Read
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}
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continue
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case werr = <-p.wclose:
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if r1 == nil {
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// finish pending Read
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p.r2 <- pipeResult{0, werr}
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r1 = p.r1 // allow another Read
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}
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if w1 == nil {
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// Close of write side during Write.
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// finish pending Write with os.EINVAL.
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p.w2 <- pipeResult{wn, os.EINVAL}
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wn = 0
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w1 = p.w1 // allow another Write
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}
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continue
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case rb = <-r1:
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if werr != nil {
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// write end is closed
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p.r2 <- pipeResult{0, werr}
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continue
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}
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if rerr != nil {
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// read end is closed
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p.r2 <- pipeResult{0, os.EINVAL}
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continue
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}
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r1 = nil // disable Read until this one is done
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case wb = <-w1:
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if rerr != nil {
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// read end is closed
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p.w2 <- pipeResult{0, rerr}
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continue
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}
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if werr != nil {
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// write end is closed
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p.w2 <- pipeResult{0, os.EINVAL}
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continue
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}
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w1 = nil // disable Write until this one is done
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}
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if r1 == nil && w1 == nil {
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// Have rb and wb. Execute.
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n := copy(rb, wb)
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wn += n
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wb = wb[n:]
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// Finish Read.
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p.r2 <- pipeResult{n, nil}
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r1 = p.r1 // allow another Read
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// Maybe finish Write.
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if len(wb) == 0 {
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p.w2 <- pipeResult{wn, nil}
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wn = 0
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w1 = p.w1 // allow another Write
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}
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}
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}
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}
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// Read/write halves of the pipe.
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// They are separate structures for two reasons:
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// 1. If one end becomes garbage without being Closed,
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// its finalizer can Close so that the other end
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// does not hang indefinitely.
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// 2. Clients cannot use interface conversions on the
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// read end to find the Write method, and vice versa.
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type pipeHalf struct {
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c1 chan []byte
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c2 chan pipeResult
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cclose chan os.Error
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done chan int
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lock sync.Mutex
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closed bool
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io sync.Mutex
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ioclosed bool
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}
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func (p *pipeHalf) rw(data []byte) (n int, err os.Error) {
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// Run i/o operation.
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// Check ioclosed flag under lock to make sure we're still allowed to do i/o.
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p.io.Lock()
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if p.ioclosed {
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p.io.Unlock()
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if p.rerr != nil {
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return 0, os.EINVAL
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}
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p.io.Unlock()
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p.c1 <- data
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res := <-p.c2
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return res.n, res.err
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}
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func (p *pipeHalf) close(err os.Error) os.Error {
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// Close pipe half.
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// Only first call to close does anything.
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p.lock.Lock()
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if p.closed {
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p.lock.Unlock()
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return os.EINVAL
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if p.data != nil {
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break
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}
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p.closed = true
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p.lock.Unlock()
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// First, send the close notification.
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p.cclose <- err
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// Runner is now responding to rw operations
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// with os.EINVAL. Cut off future rw operations
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// by setting ioclosed flag.
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p.io.Lock()
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p.ioclosed = true
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p.io.Unlock()
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// With ioclosed set, there will be no more rw operations
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// working on the channels.
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// Tell the runner we won't be bothering it anymore.
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p.done <- 1
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// Successfully torn down; can disable finalizer.
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runtime.SetFinalizer(p, nil)
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return nil
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if p.werr != nil {
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return 0, p.werr
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}
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p.rwait.Wait()
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}
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n = copy(b, p.data)
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p.data = p.data[n:]
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if len(p.data) == 0 {
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p.data = nil
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p.wwait.Signal()
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}
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return
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}
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func (p *pipeHalf) finalizer() {
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p.close(os.EINVAL)
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var zero [0]byte
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func (p *pipe) write(b []byte) (n int, err os.Error) {
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// pipe uses nil to mean not available
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if b == nil {
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b = zero[:]
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}
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// One writer at a time.
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p.wl.Lock()
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defer p.wl.Unlock()
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p.l.Lock()
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defer p.l.Unlock()
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p.data = b
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p.rwait.Signal()
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for {
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if p.data == nil {
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break
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}
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if p.rerr != nil {
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err = p.rerr
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break
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}
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if p.werr != nil {
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err = os.EINVAL
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}
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p.wwait.Wait()
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}
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n = len(b) - len(p.data)
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p.data = nil // in case of rerr or werr
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return
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}
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func (p *pipe) rclose(err os.Error) {
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if err == nil {
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err = os.EPIPE
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}
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p.l.Lock()
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defer p.l.Unlock()
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p.rerr = err
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p.rwait.Signal()
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p.wwait.Signal()
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}
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func (p *pipe) wclose(err os.Error) {
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if err == nil {
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err = os.EOF
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}
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p.l.Lock()
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defer p.l.Unlock()
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p.werr = err
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p.rwait.Signal()
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p.wwait.Signal()
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}
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// A PipeReader is the read half of a pipe.
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type PipeReader struct {
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pipeHalf
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p *pipe
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}
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// Read implements the standard Read interface:
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// it reads data from the pipe, blocking until a writer
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// arrives or the write end is closed.
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// If the write end is closed with an error, that error is
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// returned as err; otherwise err is nil.
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// returned as err; otherwise err is os.EOF.
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func (r *PipeReader) Read(data []byte) (n int, err os.Error) {
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return r.rw(data)
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return r.p.read(data)
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}
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// Close closes the reader; subsequent writes to the
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@ -231,15 +136,13 @@ func (r *PipeReader) Close() os.Error {
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// CloseWithError closes the reader; subsequent writes
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// to the write half of the pipe will return the error err.
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func (r *PipeReader) CloseWithError(err os.Error) os.Error {
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if err == nil {
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err = os.EPIPE
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}
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return r.close(err)
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r.p.rclose(err)
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return nil
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}
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// A PipeWriter is the write half of a pipe.
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type PipeWriter struct {
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pipeHalf
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p *pipe
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}
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// Write implements the standard Write interface:
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@ -248,7 +151,7 @@ type PipeWriter struct {
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// If the read end is closed with an error, that err is
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// returned as err; otherwise err is os.EPIPE.
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func (w *PipeWriter) Write(data []byte) (n int, err os.Error) {
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return w.rw(data)
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return w.p.write(data)
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}
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// Close closes the writer; subsequent reads from the
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@ -260,10 +163,8 @@ func (w *PipeWriter) Close() os.Error {
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// CloseWithError closes the writer; subsequent reads from the
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// read half of the pipe will return no bytes and the error err.
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func (w *PipeWriter) CloseWithError(err os.Error) os.Error {
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if err == nil {
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err = os.EOF
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}
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return w.close(err)
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w.p.wclose(err)
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return nil
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}
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// Pipe creates a synchronous in-memory pipe.
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@ -272,34 +173,10 @@ func (w *PipeWriter) CloseWithError(err os.Error) os.Error {
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// Reads on one end are matched with writes on the other,
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// copying data directly between the two; there is no internal buffering.
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func Pipe() (*PipeReader, *PipeWriter) {
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p := &pipe{
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r1: make(chan []byte),
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r2: make(chan pipeResult),
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w1: make(chan []byte),
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w2: make(chan pipeResult),
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rclose: make(chan os.Error),
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wclose: make(chan os.Error),
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done: make(chan int),
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}
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go p.run()
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// NOTE: Cannot use composite literal here:
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// pipeHalf{c1: p.cr1, c2: p.cr2, cclose: p.crclose, cdone: p.cdone}
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// because this implicitly copies the pipeHalf, which copies the inner mutex.
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r := new(PipeReader)
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r.c1 = p.r1
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r.c2 = p.r2
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r.cclose = p.rclose
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r.done = p.done
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runtime.SetFinalizer(r, (*PipeReader).finalizer)
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w := new(PipeWriter)
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w.c1 = p.w1
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w.c2 = p.w2
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w.cclose = p.wclose
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w.done = p.done
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runtime.SetFinalizer(w, (*PipeWriter).finalizer)
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p := new(pipe)
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p.rwait.L = &p.l
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p.wwait.L = &p.l
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r := &PipeReader{p}
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w := &PipeWriter{p}
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return r, w
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}
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