Modern Chan Channel Channel

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Channel

Holds a typed queue between goroutines; copies share it, and a new one is nil.

Syntax

Channel( of T )( [ capacity ] )

Notes

• A capacity of 0 is a RENDEZVOUS, not a zero-length buffer. Send blocks until a receiver takes the value, and the value is handed over directly rather than through the buffer -- which makes the rendezvous an ordering point as well as a handoff.
• Copies SHARE. A Channel is a refcounted handle to a channel, not a channel. Handing a copy to each of four workers gives four handles on one queue, which is what makes fan-out work. Deliberately unlike containers.Array, whose copy is deep.
• A default-constructed channel is NIL, and a nil channel blocks forever on Send and Receive. That is Go's rule, and IsNil exists so a program can assert its own initialisation -- "my program hangs" is the symptom of forgetting it.
• The destructor does not Close. Closing means "no more values will be sent", and a scope that merely stopped holding a reference has not said that.
• Requires -mt; the header refuses to compile without it.

Examples

#import "std/tasks"
using tasks

dim ch as Channel( of int32 ) = Channel( of int32 )( 4 )

print ch.Capacity( )         '' 4
print ch.IsNil( )            '' false -- constructed, not default

dim as int32 v = 42
ch.TrySend( v )
print ch.Count( )            '' 1

dim as int32 got
ch.TryReceive( got )
print got                    '' 42

'' A DEFAULT-CONSTRUCTED channel is nil, and blocks forever if used
dim nilch as Channel( of int32 )
print nilch.IsNil( )         '' true

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Library: Goroutines and Channels
Category: Goroutines and Channels
Documented under: Members