NaviServer - programmable web server
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ns_sockselect(n) 5.0.0a naviserver "NaviServer Built-in Commands"

Name

ns_sockselect - Determine readable file id's

Table Of Contents

Synopsis

Description

ns_sockselect uses a select() call to determine which file id's re readable, writable, or have exceptional conditions. ns_sockselect returns a list of three lists of: readable file id's, writable file id's, and file id's with exceptions. The -timeout option specifies the length of time to wait in seconds for ns_sockselect to return before timing out. The rfds, wfds, and efds arguments are lists of readable file id's, writable file id's, and file id's with exceptions, respectively.

COMMANDS

ns_sockselect ?timeout? rfds wfds efds

EXAMPLES

 # Start nonblocking connect()'s to www01 through
 # www09.foo.com and remember the read fileid which
 # corresponds to each write fileid.
 
 for {set n 1} {$n < 10} {incr n} {
   set host [format "www%2d.foo.com" $n]
   set fds [ns_sockopen -nonblock $host 80]
   set r [lindex $fds ]
   set w [lindex $fds 1]
   set w2r($w) $r
   lappend wfds $w
 }
 
 # All connect()'s are in progress, use select to wait for one or
 # more to become writable in the next two seconds which means 
 # they may have connected.  We're not interested in readable or
 # exception sockets so the corresponding lists are empty
 # (i.e., {}).
 
 set sel [ns_sockselect -timeout 2 {} $wfds {}]
 
 # Select returned - get the sockets ready to write to.
 
 set wfds [lindex $sel 1]
 
 # Use ns_sockcheck to see if the sockets actually connected and
 # didn't become writable because the connect() failed (e.g., no
 # Web server was running on port 80 on the corresponding machine).
 # Note that the wfds list may be empty, meaning all sockets timed
 # out on connect.
 
 set ok ""
 
 foreach w $wfds {
   if [ns_sockcheck $w] {
     # Socket is connected - send a GET HTTP request.
     lappend ok $w
     puts $w "GET /index.htm HTTP/1.0\r\n\r"
 
     # The flush is important, otherwise the remote
     # server may never see the data.
     flush $w
   }
 }
 
 # Get the read ids for each socket which we sent the GET request to.
 
 foreach w $ok {
   lappend rfds $w2r($w)
 }
 
 # Use select again to wait for the read sockets to have data
 # available in response to the GET request.
 
 set sel [ns_sockselect -timeout 2 $rfds {} {}]
 set rfds [lindex $sel 0]
 
 # Read the pages which came back.
 
 foreach r $rfds {
   if [ns_sockcheck $r] {
     set page($r) [read $r]
   }  
 }
 
 # Close all the sockets
 
 foreach w [array names w2r] {
   close $w
   close $w2r($w)
 }

See Also

nsd

Keywords

NaviServer, global built-in, socket