Passing an array to a TThread function

[tudi_x]

Hi!
I am trying to pass an array to the constructor of the class that I would be using as thread in the unit below.
Copying the array with a for loop would decrease the execution time so I would not consider it as an option.
I am getting error: 'find.pas(77,14) Error: Incompatible types: got "{Open} Array Of DictionaryEntry" expected "FindName.{Dynamic} Array Of DictionaryEntry"'.

I am trying to follow up the 'http://wiki.freepascal.org/Example_of_multi-threaded_application:_array_of_threads' tutorial.
I have read the forum entry 'http://forum.lazarus.freepascal.org/index.php?topic=24853.0' but did not understand much.

Please advise how I could pass the array to the thread constructor.

Thank you

Code: Pascal  [Select][+][-]

1. UNIT find;
2.  
3. {$mode objfpc}{$H+}
4.  
5. INTERFACE
6.  
7. USES
8. Classes, SysUtils, structures, utils, strutils;
9.  
10. TYPE
11. FindName = CLASS(TThread)
12. private
13.   _Name   : NameEntry;
14.   _Dictio   : ARRAY OF DictionaryEntry;
15.  
16. protected
17.   PROCEDURE Execute; override;
18. public
19.   PROPERTY Terminated;
20.   CONSTRUCTOR Create(VAR AName : NameEntry;var Dictio : ARRAY OF DictionaryEntry);
21. END;
22.  
23. IMPLEMENTATION
24.  
25. PROCEDURE FindName.Execute;
26. VAR
27.   i, j : INTEGER;
28.   u : Util;
29.   exname : TStringArray;
30.   isfound : BOOLEAN;
31.   buf_name : STRING;
32.  
33. BEGIN
34.   u := Util.Create;
35.   exname := u.ExplodeString(' ', _Name.FullName, 99);
36.   u.Free;
37.  
38.   FOR i := 0 TO Length(exname) - 1 DO
39.   BEGIN
40.  
41.     buf_name := trim(exname[i]);
42.  
43.     IF Length(trim(buf_name)) > 1 THEN
44.     BEGIN
45.  
46.       j := 0;
47.       isfound := False;
48.  
49.       FOR j := 0 TO Length(_Dictio) - 1 DO
50.         IF AnsiContainsText(_Dictio[j].Name, exname[i]) THEN
51.         BEGIN
52.           isfound := True;
53.           break;
54.         END;
55.  
56.       IF not isfound THEN
57.         _Name.Issue := _Name.Issue + '|Not Found: ' + exname[i];
58.     END;
59.  
60.   END;
61. END;
62.  
63.  
64. CONSTRUCTOR FindName.Create(VAR AName : NameEntry;var Dictio : ARRAY OF DictionaryEntry);
65. BEGIN
66.   _Name := AName;
67.   SetLength(_Dictio, Length(Dictio));
68.   _Dictio := Dictio;
69. END;
70.  
71. END.
72.  

structures as below:

Code: Pascal  [Select][+][-]

1. UNIT structures;
2.  
3. {$mode objfpc}{$H+}
4.  
5. INTERFACE
6.  
7. USES
8. Classes, SysUtils;
9.  
10. TYPE
11. NameEntry = RECORD
12.   FullName: STRING;
13.   Issue: STRING;
14. END;
15.  
16. TYPE
17. DictionaryEntry = RECORD
18.   Name: STRING;
19.   TypeOfEntry: INTEGER;
20. END;
21.  
22. type
23.   TStringArray = array of string;
24.  
25. IMPLEMENTATION
26.  
27. END.
28.  
29.  

[molly]

Code: [Select]

_Dictio   : ARRAY OF DictionaryEntry;
is a dynamic array, whilst Dictio in the following declaration

Code: [Select]

CONSTRUCTOR Create(VAR AName : NameEntry;var Dictio : ARRAY OF DictionaryEntry);
is an open array

See also here with a (workable) example here (sorry i was unable to find a wiki entry or something related in online fpc manual.

So, you solve it by creating a new type for the array, which is then to be used everywhere when addressing, just like your TStringArray definition.

PS: afaik the setlength isn't necessary.

[tudi_x]

I created

Code: Pascal  [Select][+][-]

1. TYPE
2. Dictionary = ARRAY OF DictionaryEntry;  
3.  

and it worked.
Thank you!

[tudi_x]

I modified my code as per attached.
When debugging I get an invalid pointer operation at the line that refers to the thread local array variable:

Code: Pascal  [Select][+][-]

1. CONSTRUCTOR FIND.Create(AName : STRING; ASentence : TJustWords);
2. BEGIN
3.   FreeOnTerminate := False;
4.  
5.   _name := AName;
6.   SetLength(_sentence, Length(ASentence));
7.   _sentence := ASentence;
8.   _isfound := False;
9.   _isready := False;
10.  
11.   INHERITED Create(False);
12. END;
13.  

Please advise what I am missing.

[molly]

You're passing along a pointer of the array. e.g. your 'local' copy is actually pointing to the global array.

e.g. guess/check what _sentence := ASentence; actually does

[tudi_x]

I am a beginner. I did not work with pointers yet.
I did not understand what I would need to modify.
Could you please detail more what I would need to modify?

[molly]

I am a beginner. I did not work with pointers yet.

Which is no excuse for not applying the basics 

I did not understand what I would need to modify.
Could you please detail more what I would need to modify?

Let's start with something fundamental and change:

Code: Pascal  [Select][+][-]

1.         IF vloop > Length(n) - 1 THEN
2.           searches[j] := f.Create(n[i], s)   //do not use threads for this case
3.         ELSE
4.           searches[j] := f.Create(n[i + j], s);
5.  

into

Code: Pascal  [Select][+][-]

1.         IF vloop > Length(n) - 1 THEN
2.           searches[j] := find.Create(n[i], s)   //do not use threads for this case
3.         ELSE
4.           searches[j] := find.Create(n[i + j], s);
5.  

At least that lets the threads run 

Drats, now the main program will not stop running.

So, taking a closer look at:

Code: Pascal  [Select][+][-]

1. PROCEDURE FIND.Execute;
2. VAR
3.   i : INTEGER;
4.  
5. BEGIN
6.   FOR i := 0 TO Length(_sentence) - 1 DO
7.     IF AnsiContainsText(_sentence[i], _name) THEN
8.     BEGIN
9.       _isfound := True;
10.       exit;
11.     END;
12.  
13.   _isready := True;
14. END;
15.  

Which makes the following check fail:

Code: Pascal  [Select][+][-]

1.       {Wait for threads to finish}
2.       WHILE no_threads_ready <> no_threads DO
3.       BEGIN
4.         no_threads_ready := 0;
5.         j := 0;
6.  
7.         FOR j := 0 TO no_threads - 1 DO
8.           IF searches[j].IsReady THEN
9.             no_threads_ready := no_threads_ready + 1;
10.  
11.       END;
12.  

Can you spot the why ?

[tudi_x]

I think because of the exit.
In case the Execute is run it will not reach _isready := True;.

I have commented the exit but searches[j].IsReady does not seem to become true.
What would be the cause?

[tudi_x]

I switched from the debugger to writeln and it looks like the IsReady property is updated.
I think it works now. The updated version of the code is attached.

Thank you for the help.

[molly]

I think because of the exit.

That is indeed correct.

If you have found the text you are searching for and then do an exit, the thread is actually finished (which is the usual way of detecting if your thread is... well... finished  )

So by not setting the _isready property value, the loop which checks if all your threads are 'done', never meets the conditions you are checking for.

Indeed if you remove the exit (or set the _isready value when you've found the text and then exit), things will begin to start working as intended.

Have fun !