Limbo supports concurrent communication and synchronization between processes via channels and a few structures working in tandem with channels.
The design for channels is inspired primarily by "Communicating Sequential Processes" (CSP) by Tony Hoare.
Further reading on CSP: http://www.usingcsp.com/cspbook.pdf
This statement shows three channels being made.
done is an unbuffered channel which transports integer values.
msgChan is an unbuffered channel, instantiated using buffered channel syntax, which transports strings.
numChan is a buffered channel which transports a tuple representing an integer pair.
The spawn statement is used to create a new process running a given function, in this case summer().
This section loads number pairs from the variable i and the number 2 from 0 to 14, covering 15 total iterations. After the iterative statement completes, a (later discarded) value is passed to the channel done. The first (and only) value in msgChan is then read out and printed.
Note: Writing to a channel whose buffer (or lack thereof) is currently full is a blocking operation. Similarly, reading from a channel whose buffer (or lack thereof) is currently empty is a blocking operation.
The function summer() operates an infinite loop which operates a single alt statement which is similar to a switch-case statement which operates on the presence of values within a channel.
The three channels are used to coordinate operation between the two processes.
num is checked first and a tuple of values is pulled out: a value and a power to raise said value to. The n^p operation is shown as n**p in Limbo, with the result being added to sum's current value.
done is checked after num has no more values in its buffer. If a value is found, the sum is stringified and passed down msg and the looping condition is unset.
The default value, indicated by *=>, is used when no channels have a value, so we sleep the current process for 5ms to de-schedule ourselves in case some form of scheduling is holding up our communications.
; limbo chans.b
; chans
Sum: 0
Sum: 1
Sum: 5
Sum: 14
Sum: 30
Sum: 55
Sum: 91
Sum: 140
Sum: 204
Sum: 285
Sum: 385
Sum: 506
Sum: 650
Final sum: 650
;
- Can you pass an ADT over a channel?
- What happens if you pass a
reftype over a channel?