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 int
  89                 var e error
  90                 var tmpReadFds, tmpWriteFds syscall.FdSet
  91                 for {
  92                         // Temporary syscall.FdSet's into which the values are copied
  93                         // because select mutates the values.
  94                         tmpReadFds = *p.readFds
  95                         tmpWriteFds = *p.writeFds
  96
  97                         s.Unlock()
  98                         n, e = syscall.Select(p.maxFd+1, &tmpReadFds, &tmpWriteFds, nil, timeout)
  99                         s.Lock()
 100
 101                         if e != syscall.EINTR {
 102                                 break
 103                         }
 104                 }
 105                 if e != nil {
 106                         return -1, 0, os.NewSyscallError("select", e)
 107                 }
 108                 if n == 0 {
 109                         return -1, 0, nil
 110                 }
 111
 112                 p.nReady = n
 113                 *p.readyReadFds = tmpReadFds
 114                 *p.readyWriteFds = tmpWriteFds
 115                 p.lastFd = 0
 116         }
 117
 118         flag := false
 119         for i := p.lastFd; i < p.maxFd+1; i++ {
 120                 if syscall.FDIsSet(i, p.readyReadFds) {
 121                         flag = true
 122                         mode = 'r'
 123                         syscall.FDClr(i, p.readyReadFds)
 124                 } else if syscall.FDIsSet(i, p.readyWriteFds) {
 125                         flag = true
 126                         mode = 'w'
 127                         syscall.FDClr(i, p.readyWriteFds)
 128                 }
 129                 if flag {
 130                         if !syscall.FDIsSet(i, p.repeatFds) {
 131                                 p.DelFD(i, mode)
 132                         }
 133                         p.nReady--
 134                         p.lastFd = i
 135                         return i, mode, nil
 136                 }
 137         }
 138
 139         // Will not reach here.  Just to shut up the compiler.
 140         return -1, 0, nil
 141 }
 142
 143 func (p *pollster) Close() error {
 144         return nil
 145 }