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# ns_chan(n) 4.99.8 naviserver "NaviServer Built-in Commands"

## Name

ns_chan - Share Tcl channels between threads and interpreters

## Table Of Contents

## Synopsis

- ns_chan cleanup ?-shared?
- ns_chan create channel name
- ns_chan get name
- ns_chan list ?-shared?
- ns_chan put name

## Description

The command ns_chan lets you transfer ownership of Tcl channels between threads and interpreters within the NaviServer process. NaviServer maintains several internal tables to implement the channel-transfer capability. Each virtual server maintains a private table of shared Tcl channels which are not associated to any particular thread. Each Tcl interpreter maintains a table of currently attached shared channels. Consequently, a shared channel can be in the per-virtual-server private table, or it can be in the interpreter private table, but not both at the same time.

Furthermore, each shared channel has a user-supplied name. This name is used to track the channel handle in the tables mentioned above. By using the various ns_chan commands, you can create shared Tcl channels and move them back and forth between the current Tcl interpreter and per-virtual-server private table.

## COMMANDS

ns_chan cleanup ?-shared?

  Closes all shared channels found in the per-virtual-server private table or current Tcl interpreter table, depending on the -shared flag. If the -shared flag is not specified, this command will close all channels from the current interpreter which were attached to it by the ns_chan get command. If the -shared flag is specified, this command will close all channels from the per-virtual-server private table, i.e., all those which are currently not attached in any Tcl interpreter or thread.

ns_chan create channel name

  Given an existing Tcl channel handle, ns_chan create "unplugs" this channel from the current interpreter, and stores it under the name in the per-virtual-server private table. Any further attempt to use this channel from the current interpreter will fail by throwing a Tcl error. On success, this command will return an empty string. The command also throws an error if the channel cannot be found in the current Tcl interpreter or if an entry already exists with the same name in the per-virtual-server private table.

ns_chan get name

  Retrieves a channel from the per-virtual-server private table for the entry name and makes it available within the current interpreter. On success, the command will return the handle for the channel. This handle can be used in any regular Tcl or NaviServer command that operates on Tcl channels, like puts, read, fconfigure, etc. The command will throw an error if the channel cannot be plugged in for current interpreter or if the entry name could not be found in the per-virtual-server private table.

ns_chan list ?-shared?

  Returns a list of all shared channels found in the per-virtual-server private table or current Tcl interpreter, depending on the -shared flag. If the -shared flag is not specified, this command will report all channels from the current interpreter which were attached to it by the ns_chan get command. If the -shared flag is specified, this command will report all channels from the per-virtual-server private table, i.e., all those which are currently not attached in any Tcl interpreter or thread.

ns_chan put name

  Unplugs a channel from the current interpreter matching entry name and returns it to the per-virtual-server private table. Any further attempt to use the named channel from the current interpreter will fail by throwing a Tcl error. On success, command will return an empty string. The command will also throw an error if the named channel was never attached to the current interpreter by some previous ns_chan get command or if the entry name is already found in the per-virtual-server private table.

## EXAMPLES

        # In thread #1, create the shared entry.
        ns_chan create [open /tmp/ns_chan w] test

        # Attach to it in thread #1, and write something to it.
        set fd [ns_chan get test]
        puts $fd "this is thread #1"

        # Detach from it in thread #1.
        ns_chan put test

        # Now, in thread #2, attach to the channel and write something to it.
        set fd [ns_chan get test]
        puts $fd "this is thread #2"

        # See it in the attached state in thread #2.
        ns_chan list ;# => test

        # Detach from it in thread #2.
        ns_chan put test

        # See it back in the per-virtual-server private table.
        ns_chan list -shared ;# => test

## See Also

ns_conn, ns_connchan

## Keywords

channels