ns_thread(3) commands


ns_thread begin script

ns_thread begindetached script

ns_thread get

ns_thread getid

ns_thread wait tid

ns_thread yield


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.


This example is similar to the example under the ns_sockselect function 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/1.0r"
    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 simpler 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 can be a problem if you plan to create many threads.