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Posix IPC-backed ASGI channel layer implementation

Project description

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An ASGI channel layer that uses POSIX shared memory IPC as its backing store (only works between processes on the same machine).

IPC is still a bit of a rough area of UNIX compatability, so if you find weird errors, please file an issue with details and exact system specifications.

Usage

You’ll need to instantiate the channel layer with a path prefix to create IPC objects underneath; any channel layers with the same prefix will talk to each other as long as they’re on the same machine.

Example:

channel_layer = IPCChannelLayer(
    prefix="aeracode",
    channel_memory=200 * 1024 * 1024,
)

prefix

Prefix to use for IPC objects under the root namespace. Defaults to asgi. IPC layers on the same machine with the same prefix will talk to each other.

channel_memory

The amount of shared memory to allocate to the channel storage, in bytes. Defaults to 100MB. All of your in-flight messages must fit into this, otherwise you’ll get ChannelFull errors if the memory space is full up.

ASGI messages can be a maximum of one megabyte, and are usually much smaller. The IPC routing metadata on top of each message is approximately 50 bytes.

group_memory

The amount of shared memory to allocate to the group storage, in bytes. Defaults to 20MB. All of your group membership data must fit into this space, otherwise your group memberships may fail to persist.

You can fit approximately 4000 group-channel membership associations into one megabyte of memory.

expiry

Message expiry in seconds. Defaults to 60. You generally shouldn’t need to change this, but you may want to turn it down if you have peaky traffic you wish to drop, or up if you have peaky traffic you want to backlog until you get to it.

group_expiry

Group expiry in seconds. Defaults to 86400. Interface servers will drop connections after this amount of time; it’s recommended you reduce it for a healthier system that encourages disconnections.

capacity

Default channel capacity. Defaults to 100. Once a channel is at capacity, it will refuse more messages. How this affects different parts of the system varies; a HTTP server will refuse connections, for example, while Django sending a response will just wait until there’s space.

channel_capacity

Per-channel capacity configuration. This lets you tweak the channel capacity based on the channel name, and supports both globbing and regular expressions.

It should be a dict mapping channel name pattern to desired capacity; if the dict key is a string, it’s intepreted as a glob, while if it’s a compiled re object, it’s treated as a regular expression.

This example sets http.request to 200, all http.response! channels to 10, and all websocket.send! channels to 20:

channel_capacity={
    "http.request": 200,
    "http.response!*": 10,
    re.compile(r"^websocket.send\!.+"): 20,
}

If you want to enforce a matching order, use an OrderedDict as the argument; channels will then be matched in the order the dict provides them.

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