Simple, thread safe shell-pipe like abstraction for queues.

REVIEWS WANTED

Check this repository out recursively, add include/ and vendor/concurrentqueue/ to your include paths.

#include "softwear/concurrent_channel.hpp"
// Holding 80K elements, polling every half millisecond
softwear::concurrent_channel<int>{80000, 500};

Taken from the API documentation; in case of doubt, the API doc is authoritative

Beyond a basic concurrent queue functionality, this provides flow control and end-of-transmission signaling between threads, specifically:

• Support for a simple capacity limit
• Support for enqueue methods that block if the channel is at capacity
• Support for dequeue methods that block if no data is available in the channel
• Support for a close() method and an eof() check to allow provider threads to signal that there is no more data to process.
• Iterator support

Taken from the API documentation; in case of doubt, the API doc is authoritative

Moodycamel's pipe is excellent, but a bit complex to use:

Why a simple capacity limit? Personally, I implemented this for an application that red data via network, ran some heavy computation on the data then sent it to another network host: I started a couple of IO threads for loading, a couple to send the processed data and a couple for the actual processing, with a channel between each step. If fetching or the data processing where slow, the other threads would implicitly wait for them. If the processing or fetching where to fast, they would automatically stop and wait for the other threads, so no thread can fill up all the ram.

Why close signaling? After the last fetching thread is done, it signals that the job is done to processing; processing in turn can forward the signal to the uploader, so in the management thread very little effort is needed: It needs to set up the channel and start the threads, then it just need to join() all the threads and exit as soon as all the threads are don.

See tests.cc for an example.

include/softwear/concurrent_queue.hpp contains detailed documentation.

Run make.

concurrent_channel supports iterators for dequeueing through begin() and end() and it supports enqueueing via the channel.iwrite range. However, due to it's concurrent nature and due to the fact that you can't peek (look at an element without dequeuing it), there are some limitations; from the documentation:

Range for enqueueing elements.

In general, using end() can't be relied on; take the following code for instance: i == end(); *i = something; is the same as c.eof(); c.enqueue(i). This code checks whether the channel has ended, but even if that check succeeds, the channel may still be closed between the check and calling enqueue, so the assignment could throw closed. Any sequence of calls other than assingment; increment; assignment; ... results in undefined behaviour.

The iterators are invalidated by moving the queue into a different container.

Range that can be used to read from the channel with iterators.

*(++i) on the iterator is equivalent to a call to dequeue

Comparing the iterator with end() or dereferencing it will dequeue one element and store it in the iterator. If you don't use it afterwards, it will be lost. This can happen easily for instance when using a for-in loop, since the for-in loop will compare with end() implicitly before running the code block. This also means that a comparison with end() might block.

The iterators are invalidated by moving the queue into a different container.

• Allocator support (doable through the malloc/free in the Traits)
• Locking based implementation
• More precise size computation for the internal queue (avoiding malloc)
• Update the documentation to reflect all information from Concurrentqueue
• Reviews

Written by ([email protected]) Karolin Varner, for Softwear, BV (http://nl.softwear.nl/contact): You can still buy me a Club Mate. Or a coffee.

Copyright © (c) 2015 and 2016, Softwear, BV. All rights reserved.

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