Pooled Channel in Local or Shared memory
Emanuele Ruffaldi 2014-2016
Conceptually similar to Python Queue
Bonus Shared memory
Bonus reader/writer scheme for large objects
Usage
Template <T, container > allows to specify the container (vector or list or array). Default is vector
Constructor
Constructor specifies the policy:
PooledChannel(int n, bool adiscardold, bool aalwayslast)
- n is the size of the buffer, n<=0 means infinite queue, but only if the container is not array<T,q>, otherwise use array size
- adiscardold means that on overflow discard old data, otherwise discard new data
- aalwayslast means that return only last one
Usage
- write(const T &)
- read(T &) returns bool
- readNoWait(T&)
- readySize() returns available data for read
- freeSize() returns available data for write
In addition there is the transactional API
IPC
IPC Pooled Channel is provided using boost interprocess:
- pool of multiple blocks
- client connects to the pool and verifies type and buffer size
- 1 reader and 1 writer
For a 3 buffer exchange we have around 12us exchange time
Limitations:
- boost interprocess shared memory are dangling (see below)
- resume of writer is supported (but has to be specific marked due to the previous issues)
- starting of reader without writer is not supported
- multiple reader or multiple writer is not supported
Currently we use boost for sharing in IPC case but there are other interesting options that overcome the issues with the naming scheme of boost/Unix shared memory:
- memfd under linux + Unix socket for transferring the descriptor: https://github.com/a-darwish/memfd-examples
- mmap under OSX/Linux provides MAP_ANON that needs to be passed via fork, or rather Domain Socket (e.g. gstreamer https://github.com/GStreamer/gst-plugins-bad/blob/master/sys/shm/gstshmsrc.c)
- CreateFileMapping with invalid HANDLE is similar, then passed via CreateProcess inheritance or alternatively DuplicateHandle
TODO
Make examples similar to Go channels
TODO Regular
- implement the lockfree scheme of boost using C++11 policy