Tcl API Reference -- ns_thread

### ns_thread

#### Overview

Manage threads

#### Syntax

ns_thread begin script

ns_thread begindetached script

ns_thread get

ns_thread getid

ns_thread wait tid

ns_thread yield

#### Description

ns_thread begin begins a new thread which evaluates the specified script and then exits. It returns a thread ID that must eventually be passed to ns_thread wait. (Failing to call ns_thread wait will eventually result in no new threads being created.)

ns_thread begindetached begins a detached thread that doesn't have to be (and can't be) waited for.

ns_thread get gets the thread ID of the current thread. The result is a thread ID that can be passed to ns_thread wait and may look something like "tid532".

ns_thread getid gets the thread integer number for the current thread. The result is a small integer used for identifying threads is a human-readable way, such as "1" or "1120", for example.

ns_thread wait waits for the specified thread to exit. The tid argument is a thread ID returned by ns_thread begin or ns_thread get.

ns_thread yield causes the current thread to yield.

#### Example

This example is similar to the example under the ns_sockselect function (see page 205) of connecting to the 10 servers and waiting to service them with the ns_sockselect command. In this case, though, each connection gets it's own thread.

        # This is the procedure which is evaluated for each thread and
        # handles a single connection to host number $i

        proc getpage {i} {
                global pages
                # new thread will start here - first connect to host
                set host [format "www%2d.foo.com" $i]
                set fds [ns_sockopen $host 80
                set r [lindex $fds 0]
                set w [lindex $fds 1]
                # next, send request
                puts $w "GET /index.htm HTTP/1.0\r\n\r"
                flush $w
                # then read page
                set pages($i) [read $r]
                # and close sockets
                close $w
                close $r
                # thread goes away here and other threads waiting
                # on ns_thread wait will wakeup
        }

        # Here's the loop which creates the threads which run getpage.
        for {set i 1} {$i < 9} {incr i} {
                set tids($i) [ns_thread begin "getpage $i"]
        }

        # wait for the threads to exit and then process the pages
        for {set i 1} {$i < 9} {incr i} {
                ns_thread wait $tids($i)
                # output page
                ... process the page in $pages($i) put there by other
        			thread ...
        }

Note that the code here is much simplier to follow than the ns_sockselect example; that's the benefit of multithreaded programming. However, it uses more resources as threads need to be created and initialized. This is generally not a problem unless you plan to create many threads.

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