| Description |
The IsMultiThread function returns true when there is at least one thread running in addition to the main line of execution.
Threads are a complex matter (the example is a very simple example, but is still not so short), and beyond detailed discussion here.
Threads can be started using BeginThread as in the example, or using the TThread class.
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| Related commands |
| BeginThread |
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Begins a separate thread of code execution |
| EndThread |
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Terminates a thread with an exit code |
| ThreadVar |
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Defines variables that are given separate instances per thread |
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| Example code : A simple example |
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
unit Unit1;
interface
uses
Forms, Dialogs, Windows, SysUtils;
type
TMsgRecord = record
msg : string[30];
end;
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
end;
var
Form1: TForm1;
Implementation
{$R *.dfm} // Include form definitions
ThreadVar // We must allow each thread its own instances
// of the passed record variable
msgPtr : ^TMsgRecord;
// Private thread procedure to show a string
function ShowMsg(Parameter : Pointer) : Integer;
begin
// Set up a 0 return value
Result := 0;
// Map the pointer to the passed data
// Note that each thread has a separate copy of msgPtr
msgPtr := Parameter;
// Display this message
ShowMessagePos('Thread message : '+msgPtr.msg, 200, 100);
// End the thread
EndThread(0);
end;
procedure TForm1.FormCreate(Sender: TObject);
var
id1 : LongWord;
thread1 : Integer;
msg1 : TMsgRecord;
showMsgFunc : TThreadFunc;
begin
// Set up the thread function
showMsgFunc := Addr(ShowMsg);
// Set up our display messages
msg1.msg := 'Hello World';
// Inidicate that we are not running a thread
if IsMultiThread
then WriteLn('Multi-threaded')
else WriteLn('Single threaded');
// Start the first thread running asking for users first name
thread1 := BeginThread(nil,
0,
showMsgFunc,
Addr(msg1),
0,
id1);
// Inidicate that we are running a thread
if IsMultiThread
then WriteLn('Multi-threaded')
else WriteLn('Single threaded');
// Ensure that the thread is only closed when all done
ShowMessagePos('Press this when thread dialog finished.', 200, 300);
// Finally, tidy up by closing the threads
CloseHandle(thread1);
end;
end.
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A sequence of dialogs is displayed:
Single threaded
Multi-threaded + Thread message : Hello World
Press this when the thread dialog finished.
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