[SOLVED] TStringList.free does not really release memory?

[senglit]

Hi all,

I have a procedure which is to find some files' location in a folder. The structure of the folder is already known so that I used some TStringList to store the result of each step. There are more than 20,000 subfolders in the sRootDir. And the number of subfolders will grows up very quickly(aroud 500 more per day). So I checked carefull if I use TStringList.Free procedure.

But still, every time when this procedure is called (around 1 time per 1 minute), I can see the used memory growing quickly (90MByte more after each calling) in windows task manager.

Please help me to check if I made some stupid mistakes. Thanks

Code: Pascal  [Select][+][-]

1. procedure SearchFile(sRootDir: string);
2. var
3.   Found: integer;
4.   SearchRec: TSearchRec;
5.   i,j:integer;
6.   SiteFolders,DayFolders,HourFolders,AudioFolders: TStringList;
7. begin
8.   SiteFolders:=TStringList.Create;  
9.   DayFolders:=TStringList.Create;
10.   HourFolders:=TStringList.Create;
11.   AudioFolders:=TStringList.Create;
12.   DoneFileList.Clear;
13.   AudioFileList.Clear;
14.   DataFileList.Clear;
15.   Found := FindFirst(sRootDir + '\*', faDirectory, SearchRec);    
16.   while Found = 0 do
17.   begin
18.     if  (SearchRec.Name <> '.') and  (SearchRec.Name <> '..') then
19.     begin
20.       SiteFolders.Add(sRootDir + '\'+SearchRec.Name);
21.     end;
22.     Found := FindNext(SearchRec);
23.   end;
24.   FindClose(SearchRec);
25.  
26.   for i:=0 to SiteFolders.Count-1 do
27.   begin
28.     Found := FindFirst(SiteFolders[i]+'\*', faDirectory, SearchRec);    
29.     while Found = 0 do
30.     begin
31.       if  (SearchRec.Name <> '.') and  (SearchRec.Name <> '..') then
32.       begin
33.         DayFolders.Add(SiteFolders[i]+'\'+SearchRec.Name);
34.       end;
35.       Found := FindNext(SearchRec);
36.     end;
37.   end;
38.   FindClose(SearchRec);
39.  
40.   for i:=0 to DayFolders.Count-1 do
41.   begin
42.     Found := FindFirst(DayFolders[i]+'\*', faDirectory, SearchRec);    
43.     while Found = 0 do
44.     begin
45.       if  (SearchRec.Name <> '.') and  (SearchRec.Name <> '..') then
46.       begin
47.         HourFolders.Add(DayFolders[i]+'\'+SearchRec.Name);
48.       end;
49.       Found := FindNext(SearchRec);
50.     end;
51.   end;
52.   FindClose(SearchRec);
53.  
54.   for i:=0 to HourFolders.Count-1 do
55.   begin
56.     Found := FindFirst(HourFolders[i]+'\*', faAnyFile, SearchRec);
57.     while Found = 0 do
58.     begin
59.       if (SearchRec.Attr = faDirectory) then
60.       begin
61.          if (SearchRec.Name = 'Audio') then            
62.          begin
63.            AudioFolders.Add(HourFolders[i]+'\'+SearchRec.Name);
64.          end;
65.       end
66.       else begin                                    
67.         for j:=0 to DATA_TYPES.Count-1 do
68.         begin
69.           if (DATA_TYPES[j]+'.bid' = SearchRec.Name) then                        
70.             if FileExists(HourFolders[i]+'\'+SearchRec.Name+'.done') then        
71.             begin
72.               DoneFileList.Add(HourFolders[i]+'\'+SearchRec.Name+'.done');
73.             end
74.             else begin
75.               DataFileList.Add(HourFolders[i] + '\' + SearchRec.Name);
76.               Inc(DataFileCount);
77.             end;
78.         end;
79.       end;
80.       Found := FindNext(SearchRec);
81.     end;
82.   end;
83.   FindClose(SearchRec);
84.  
85.   for i:=0 to AudioFolders.Count-1 do
86.   begin
87.     Found := FindFirst(AudioFolders[i]+'\*', faAnyFile, SearchRec);
88.     while Found = 0 do
89.     begin
90.       if RightStr(SearchRec.Name,4)='.bid' then                              
91.         if FileExists(AudioFolders[i]+'\'+SearchRec.Name+'.done') then      
92.         begin
93.           DoneFileList.Add(AudioFolders[i]+'\'+SearchRec.Name+'.done');
94.         end
95.         else begin
96.           AudioFileList.Add(AudioFolders[i] + '\' + SearchRec.Name);
97.         end;
98.       Found := FindNext(SearchRec);
99.     end;
100.   end;
101.   FindClose(SearchRec);
102.  
103.   SiteFolders.Free;
104.   DayFolders.Free;
105.   HourFolders.Free;
106.   AudioFolders.Free;
107. end;            
108.  

DoneFileList, DataFileList and AudioFolders are global vars.

[bytebites]

Code: Pascal  [Select][+][-]

1.  
2.   for i:=0 to SiteFolders.Count-1 do
3.   begin
4.     Found := FindFirst(SiteFolders[i]+'\*', faDirectory, SearchRec);    
5.     while Found = 0 do
6.     begin
7.       if  (SearchRec.Name <> '.') and  (SearchRec.Name <> '..') then
8.       begin
9.         DayFolders.Add(SiteFolders[i]+'\'+SearchRec.Name);
10.       end;
11.       Found := FindNext(SearchRec);
12.     end;
13.     FindClose(SearchRec);<-- move within for loop
14.   end;
15.  
16.  

[furious programming]

Shorter, safer and more readable usage of the FindFirst, FindNext and FindClose looks like this:

Code: Pascal  [Select][+][-]

1. if FindFirst({parameters}) = 0 then
2. try
3.   repeat
4.     {usage of the found item}
5.   until FindNext({parameter}) <> 0;
6. finally
7.   FindClose({parameter});
8. end;

Follow this schema — you will avoid memory leaks.

[senglit]

Code: Pascal  [Select][+][-]

1.  
2.   for i:=0 to SiteFolders.Count-1 do
3.   begin
4.     Found := FindFirst(SiteFolders[i]+'\*', faDirectory, SearchRec);    
5.     while Found = 0 do
6.     begin
7.       if  (SearchRec.Name <> '.') and  (SearchRec.Name <> '..') then
8.       begin
9.         DayFolders.Add(SiteFolders[i]+'\'+SearchRec.Name);
10.       end;
11.       Found := FindNext(SearchRec);
12.     end;
13.     FindClose(SearchRec);<-- move within for loop
14.   end;
15.  
16.  

It works perfectly! Thank you.

But I'm still confused that even I put this FindClose at wrong pace, I still called it before the procedure is finished. So, the used memory will growing when the procedure is called, but it should be released before the 'end;'. Maybe there is something I don't know about TSearchRec?

[senglit]

Shorter, safer and more readable usage of the FindFirst, FindNext and FindClose looks like this:

Code: Pascal  [Select][+][-]

1. if FindFirst({parameters}) = 0 then
2. try
3.   repeat
4.     {usage of the found item}
5.   until FindNext({parameter}) <> 0;
6. finally
7.   FindClose({parameter});
8. end;

Follow this schema — you will avoid memory leaks.

Yes it looks more beautifull indeed. Thanks!

[PascalDragon]

But I'm still confused that even I put this FindClose at wrong pace, I still called it before the procedure is finished. So, the used memory will growing when the procedure is called, but it should be released before the 'end;'. Maybe there is something I don't know about TSearchRec?

Each call to FindFirst results in the creation of a new TSearchRec. The function does not care about what you pass in, so a previously initialized TSearchRec will leak. As you did so in your loop each loop run except for the last you leaked a TSearchRec.

[furious programming]

In addition, if you iterate over all the elements of a given collection (e.g. list or array), you can use the for in loop — it will be easier to use the iterator, and the code itself will be shorter. So, in summary, you can do it in this way:

Code: Pascal  [Select][+][-]

1. var
2.   Folder: String;
3.  
4. {..}
5.  
6. for Folder in SiteFolders do
7.   if FindFirst(Folder + '\*', faDirectory, SearchRec) = 0 then
8.   try
9.     repeat
10.       if (SearchRec.Name <> '.') and (SearchRec.Name <> '..') then
11.         DayFolders.Add(Folder + '\' + SearchRec.Name);
12.     until FindNext(SearchRec) <> 0;
13.   finally
14.     FindClose(SearchRec);
15.   end;

[senglit]

In addition, if you iterate over all the elements of a given collection (e.g. list or array), you can use the for in loop — it will be easier to use the iterator, and the code itself will be shorter. So, in summary, you can do it in this way:

Code: Pascal  [Select][+][-]

1. var
2.   Folder: String;
3.  
4. {..}
5.  
6. for Folder in SiteFolders do
7.   if FindFirst(Folder + '\*', faDirectory, SearchRec) = 0 then
8.   try
9.     repeat
10.       if (SearchRec.Name <> '.') and (SearchRec.Name <> '..') then
11.         DayFolders.Add(Folder + '\' + SearchRec.Name);
12.     until FindNext(SearchRec) <> 0;
13.   finally
14.     FindClose(SearchRec);
15.   end;

Rewrote the code following your instruction. It looks much beter now. Thanks