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PosixChannels.jl

Documentation for PosixChannels.jl

PosixChannels — Module

PosixChannels provides an AbstractChannel-compatible channel using POSIX message queues.

The high level API is available through PosixChannel.

For more informations on POSIX message queues, see man 7 mq_overview.

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Table of contents

Public API

PosixChannel

PosixChannels.PosixChannel — Method
PosixChannel{T}(name, kwargs...)

Create a PosixChannel that works with messages of type T.

Notes: T must be a plain data type (isbitstype must return true), and the message queue must allow for messages of at least sizeof(T).

Extended help

Arguments

See man 3 mq_open for details.

All usages

  • mode::Symbol=:rw: the opening mode of the POSIX queue, can be :r, :w, or :rw.
  • cloexec::Bool=false: Activate the O_CLOEXEC flag.
  • create::Bool=true: Activate the O_CREAT flag.
  • excl::Bool=false: Activate the O_CREAT flag.
  • nonblock::Bool=false: Activate the O_NONBLOCK flag.

Creation specifics

When creating a new queue (flag O_CREAT activated), it is necessary to provide additional informations.

  • create_r_user::Bool=true: Make queue readable for user.

  • create_w_user::Bool=true: Make queue writable for user.

  • create_r_group::Bool=true: Make queue readable for the group of the user.

  • create_w_group::Bool=true: Make queue writable for the group of the user.

  • create_r_other::Bool=false: Make queue readable for other users.

  • create_w_other::Bool=false: Make queue writable for other users.

  • create_len::Int=systemmsgdefault(): Maximum number of messages in the queue.

  • create_msg_size::Int=sizeof(T): Maximum size of a message.

Examples

Start two julia REPL (a sender and a receiver).

sender.jl:

using PosixChannels

chan = PosixChannel{Int}("posix_channels_are_fun", mode=:w)
print("Press [Enter] when you are ready to send data.")
readline()

for i in 1:10
    put!(chan, i)
end

println("Done!")
println("Closing the channel.")
close(chan)

receiver.jl

using PosixChannels

chan = PosixChannel{Int}("posix_channels_are_fun", mode=:r)
println("Listening for 10 incoming Int, you may start sending")

for _ in 1:10
    while !isready(chan)
        wait(chan)
    end
    msg = take!(chan)
    println("Received $msg")
end

println("Done!")
println("Closing the channel.")
close(chan)
println("Deleting the channel.")
unlink(chan)

You can then launch each script, and press return in the sender's window.

$ julia --project sender.jl
Press [Enter] when you are ready to send data.
Done!
Closing the channel.
$ julia --project receiver.jl
Listening for 10 incoming Int, you may start sending
Received 1
Received 2
Received 3
Received 4
Received 5
Received 6
Received 7
Received 8
Received 9
Received 10
Done!
Closing the channel.
Deleting the channel.
Types of messages

This example uses integers, but any type that verifies isbitstype could be used. See StaticStrings for example.

See also wait, put!, take!, unlink, isnonblocking.

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AbstractChannel interface

/proc utilities

The system-wide defaults for POSIX message queues can be set through a /proc interface. See man 7 mq_overview for details.

Internal API

PosixChannels.open_posix_mqueue — Function
open_posix_mqueue(name, flags[, perm, attr])

Call the C function mq_open with the given name and flags. Checks for errors using Base.systemerror. name is corrected using correct_name.

When O_CREAT flag is on, perm and attr are required.

See man 3 mq_open for details.

See also close_posix_mqueue.

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open_posix_mqueue(name; kwargs...)

Call mq_open by explicitely constructing the various flags beforehand.

Arguments

See man 3 mq_open for details.

All usages

  • mode::Symbol=:rw: the opening mode of the POSIX queue, can be :r, :w, or :rw.
  • cloexec::Bool=false: Activate the O_CLOEXEC flag.
  • create::Bool=true: Activate the O_CREAT flag.
  • excl::Bool=false: Activate the O_CREAT flag.
  • nonblock::Bool=false: Activate the O_NONBLOCK flag.

Creation specifics

When creating a new queue (flag O_CREAT activated), it is necessary to provide additional informations.

  • create_r_user::Bool=true: Make queue readable for user.

  • create_w_user::Bool=true: Make queue writable for user.

  • create_r_group::Bool=true: Make queue readable for the group of the user.

  • create_w_group::Bool=true: Make queue writable for the group of the user.

  • create_r_other::Bool=false: Make queue readable for other users.

  • create_w_other::Bool=false: Make queue writable for other users.

  • create_len::Int=systemmsgdefault(): Maximum number of messages in the queue.

  • create_msg_size::Int=systemmsgsizedefault(): Maximum size of a message.

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PosixChannels.register_notifier_cfunction — Function
register_notifier_cfunction(chan)

Call the C function mq_notify for the message queue. Checks for errors using Base.systemerror.

mq_notify is called with the SIGEV_THREAD flag and configured to call notify_channel with the channel's condition handle as a parameter. This is done so the OS will start a thread that will unlock the condition when a new message is posted to the empty queue. This function is used by wait before it starts waiting for the channel's condition.

See man 3 mq_notify for details.

See also notify_channel

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