DispatchSerialQueue minimum OS support

Question

abhishekjain OP

Created 3d

Replies 3

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Hi Team,

We intend to create a custom serial dispatch queue targetting a global queue.

let serialQueue = DispatchQueue(label: "corecomm.tallyworld.serial", target: DispatchQueue.global(qos: .default))

The documentation for DispatchQueue init does not show any minimum OS versions. BUT DispatchSerialQueue init does show iOS 17.0+ iPadOS 17.0+ Mac Catalyst macOS 14.0+ tvOS 17.0+ visionOS watchOS 10.0+.

Does that mean - I will not be able to create a custom serial dispatch queue below iOS 17?

Answered by DTS Engineer in 847526022

We intend to use it for our communication subsystem - to associate it and start [NWConnection]

OK, cool. Then I have some good news (-:

Network framework doesn’t require you to use a serial queue. The parameter for, say, connection.start(queue:) is of type DispatchQueue.

Now, using anything other than a serial queue is, of course, bananas. For a concrete example of where using a concurrent queue with Network framework caused problems, see this thread. However, the important point is that this desire to use a serial queue isn’t encoded in the type system. That is, you’re not required to use DispatchSerialQueue.

Given that, it’s fine to create a DispatchQueue for this work as long as the underlying queue is serial. So, for example, this code compiles:

let connection = NWConnection(host: "example", port: 443, using: .tls)
let queue = DispatchQueue(label: "network-queue", target: nil)
connection.start(queue: queue)

even with the deployment target set to macOS 10.14, that is, the OS release where Network framework was introduced.

And if you want to set a target queue for your serial queue, you can do that using the target parameter that I’ve left nil in this example.

ps Your example does this:

let serialQueue = DispatchQueue(…, target: DispatchQueue.global(qos: .default))

That’s weird because the default global concurrent queue is the default target for a serial queue. IMO you should only set a target if it’s something other than this default.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

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Answer 1

DTS Engineer OP

Apple

3d

This is tricky. Dispatch serial queues, the concept, have existed since the Dawn of Time™ [1]. However, DispatchSerialQueue, the Swift type, is only available on more recent systems. So, you can certainly create a Dispatch serial queue on older systems [2], but you may not be able to use it in all cases.

What are you planning to do with this serial queue?

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] Well, since the introduction of Dispatch back in macOS 10.6 / iOS 4 (-:

[2] Although if you want to target a queue, be aware that setting the target on create is done with dispatch_queue_create_with_target, which was introduced in macOS 10.12 / iOS 10. Alternatively, dispatch_set_target_queue has been around since the introduction of Dispatch.

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Answer 2

abhishekjain OP

3d

Thanks for a prompt response @DTS Engineer.

We intend to use it for our communication subsystem - to associate it and start the NWConnections and NWListeners we will be creating - for async execution of various associated handlers. We don't intend to directly use the DispatchSerialQueue, the Swift type, but as DispatchQueue object.

0

Answer 3

DTS Engineer OP

Apple

2d

Recommended

We intend to use it for our communication subsystem - to associate it and start [NWConnection]

OK, cool. Then I have some good news (-:

Network framework doesn’t require you to use a serial queue. The parameter for, say, connection.start(queue:) is of type DispatchQueue.

Now, using anything other than a serial queue is, of course, bananas. For a concrete example of where using a concurrent queue with Network framework caused problems, see this thread. However, the important point is that this desire to use a serial queue isn’t encoded in the type system. That is, you’re not required to use DispatchSerialQueue.

Given that, it’s fine to create a DispatchQueue for this work as long as the underlying queue is serial. So, for example, this code compiles:

let connection = NWConnection(host: "example", port: 443, using: .tls)
let queue = DispatchQueue(label: "network-queue", target: nil)
connection.start(queue: queue)

even with the deployment target set to macOS 10.14, that is, the OS release where Network framework was introduced.

And if you want to set a target queue for your serial queue, you can do that using the target parameter that I’ve left nil in this example.

ps Your example does this:

let serialQueue = DispatchQueue(…, target: DispatchQueue.global(qos: .default))

That’s weird because the default global concurrent queue is the default target for a serial queue. IMO you should only set a target if it’s something other than this default.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

0