What do detached and assignCurrentContext meaning?

Question

When I add a job into the queue, DispatchWorkItemFlags gives us several options to choose

public func sync<T>(flags: DispatchWorkItemFlags, execute work: () throws -> T) rethrows -> T
public static let barrier: DispatchWorkItemFlags
public static let detached: DispatchWorkItemFlags
public static let assignCurrentContext: DispatchWorkItemFlags

I know barrier makes the job not being executed the same time with others, but I don't know what detached and assignCurrentContext are, and Apple don't provide any description about them, so who can tell me about this.

Answer 1

You can read about them in the dispatch_block_flags_t manual:

DISPATCH_BLOCK_ASSIGN_CURRENT Indicates that a dispatch block should be assigned the execution context attributes that are current at the time the block object is created. …

DISPATCH_BLOCK_BARRIER Indicates that a dispatch block should act as a barrier block when submitted to a DISPATCH_QUEUE_CONCURRENT queue. …

DISPATCH_BLOCK_DETACHED Indicates that a dispatch block should execute disassociated from current execution context attributes such as QoS class, os_activity_t, and properties of the current IPC request, if any. …

I’ve only copied the first sentence from each flag’s documentation. Click the link for more details.