libgo/go/net/fd_select.go

   1 // Copyright 2010 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Waiting for FDs via select(2).
   6
   7 package net
   8
   9 import (
  10         "os"
  11         "syscall"
  12 )
  13
  14 type pollster struct {
  15         readFds, writeFds, repeatFds *syscall.FdSet
  16         maxFd                        int
  17         readyReadFds, readyWriteFds  *syscall.FdSet
  18         nReady                       int
  19         lastFd                       int
  20 }
  21
  22 func newpollster() (p *pollster, err error) {
  23         p = new(pollster)
  24         p.readFds = new(syscall.FdSet)
  25         p.writeFds = new(syscall.FdSet)
  26         p.repeatFds = new(syscall.FdSet)
  27         p.readyReadFds = new(syscall.FdSet)
  28         p.readyWriteFds = new(syscall.FdSet)
  29         p.maxFd = -1
  30         p.nReady = 0
  31         p.lastFd = 0
  32         return p, nil
  33 }
  34
  35 func (p *pollster) AddFD(fd int, mode int, repeat bool) (bool, error) {
  36         // pollServer is locked.
  37
  38         if mode == 'r' {
  39                 syscall.FDSet(fd, p.readFds)
  40         } else {
  41                 syscall.FDSet(fd, p.writeFds)
  42         }
  43
  44         if repeat {
  45                 syscall.FDSet(fd, p.repeatFds)
  46         }
  47
  48         if fd > p.maxFd {
  49                 p.maxFd = fd
  50         }
  51
  52         return true, nil
  53 }
  54
  55 func (p *pollster) DelFD(fd int, mode int) {
  56         // pollServer is locked.
  57
  58         if mode == 'r' {
  59                 if !syscall.FDIsSet(fd, p.readFds) {
  60                         print("Select unexpected fd=", fd, " for read\n")
  61                         return
  62                 }
  63                 syscall.FDClr(fd, p.readFds)
  64         } else {
  65                 if !syscall.FDIsSet(fd, p.writeFds) {
  66                         print("Select unexpected fd=", fd, " for write\n")
  67                         return
  68                 }
  69                 syscall.FDClr(fd, p.writeFds)
  70         }
  71
  72         // Doesn't matter if not already present.
  73         syscall.FDClr(fd, p.repeatFds)
  74
  75         // We don't worry about maxFd here.
  76 }
  77
  78 func (p *pollster) WaitFD(s *pollServer, nsec int64) (fd int, mode int, err error) {
  79         if p.nReady == 0 {
  80                 var timeout *syscall.Timeval
  81                 var tv syscall.Timeval
  82                 timeout = nil
  83                 if nsec > 0 {
  84                         tv = syscall.NsecToTimeval(nsec)
  85                         timeout = &tv
  86                 }
  87
  88                 var n, e int
  89                 var tmpReadFds, tmpWriteFds syscall.FdSet
  90                 for {
  91                         // Temporary syscall.FdSet's into which the values are copied
  92                         // because select mutates the values.
  93                         tmpReadFds = *p.readFds
  94                         tmpWriteFds = *p.writeFds
  95
  96                         s.Unlock()
  97                         n, e = syscall.Select(p.maxFd+1, &tmpReadFds, &tmpWriteFds, nil, timeout)
  98                         s.Lock()
  99
 100                         if e != syscall.EINTR {
 101                                 break
 102                         }
 103                 }
 104                 if e != 0 {
 105                         return -1, 0, os.NewSyscallError("select", e)
 106                 }
 107                 if n == 0 {
 108                         return -1, 0, nil
 109                 }
 110
 111                 p.nReady = n
 112                 *p.readyReadFds = tmpReadFds
 113                 *p.readyWriteFds = tmpWriteFds
 114                 p.lastFd = 0
 115         }
 116
 117         flag := false
 118         for i := p.lastFd; i < p.maxFd+1; i++ {
 119                 if syscall.FDIsSet(i, p.readyReadFds) {
 120                         flag = true
 121                         mode = 'r'
 122                         syscall.FDClr(i, p.readyReadFds)
 123                 } else if syscall.FDIsSet(i, p.readyWriteFds) {
 124                         flag = true
 125                         mode = 'w'
 126                         syscall.FDClr(i, p.readyWriteFds)
 127                 }
 128                 if flag {
 129                         if !syscall.FDIsSet(i, p.repeatFds) {
 130                                 p.DelFD(i, mode)
 131                         }
 132                         p.nReady--
 133                         p.lastFd = i
 134                         return i, mode, nil
 135                 }
 136         }
 137
 138         // Will not reach here.  Just to shut up the compiler.
 139         return -1, 0, nil
 140 }
 141
 142 func (p *pollster) Close() error {
 143         return nil
 144 }