Non Blocking Channel Operations in Pascal

Our program demonstrates non-blocking channel operations. Here’s the full source code and explanation:

program NonBlockingChannelOperations;

uses
  SysUtils, Classes;

type
  TStringChannel = class(TThreadedQueue<string>);
  TBooleanChannel = class(TThreadedQueue<Boolean>);

var
  messages: TStringChannel;
  signals: TBooleanChannel;

begin
  messages := TStringChannel.Create;
  signals := TBooleanChannel.Create;
  try
    // Non-blocking receive
    if messages.PopItem(msg, 0) then
      WriteLn('received message ', msg)
    else
      WriteLn('no message received');

    // Non-blocking send
    msg := 'hi';
    if messages.PushItem(msg, 0) then
      WriteLn('sent message ', msg)
    else
      WriteLn('no message sent');

    // Multi-way non-blocking select
    if messages.PopItem(msg, 0) then
      WriteLn('received message ', msg)
    else if signals.PopItem(sig, 0) then
      WriteLn('received signal ', BoolToStr(sig, True))
    else
      WriteLn('no activity');

  finally
    messages.Free;
    signals.Free;
  end;
end.

In this Pascal example, we use TThreadedQueue from the Classes unit to simulate channels. The PopItem and PushItem methods with a timeout of 0 are used for non-blocking operations.

Here’s a non-blocking receive. If a value is available on messages, then it will be retrieved. If not, it will immediately move to the else clause.

A non-blocking send works similarly. Here msg is attempted to be sent to the messages channel. If it can’t be sent immediately, the else clause is executed.

We can use multiple conditions to implement a multi-way non-blocking select. Here we attempt non-blocking receives on both messages and signals.

To run the program, compile it and execute the resulting binary:

$ fpc non_blocking_channel_operations.pas
$ ./non_blocking_channel_operations
no message received
no message sent
no activity

This example demonstrates how to perform non-blocking operations on channel-like structures in Pascal, providing similar functionality to select statements with default clauses in other languages.