[fpc-pascal] File handling: the TFileStream or the classical way is faster and more efficient?

[Géza Kovacs Géza]

Hi All!

What is the faster and more efficient, using the TFileStream or the
classical way ("file of byte", or "file") type with
blockread/blockwrite and the other well-know procedures?
What is the better, faster on large files?

See the two example code below.

Program FileCopy_stream;
{$mode objfpc} {$H+}
uses classes,SysUtils;
var
BytesRead,TotalBytesRead : Int64;
puffer : array [1..1048576] of byte;
InF, OutF : TFileStream;
begin
TotalBytesRead := 0;
BytesRead := 0;
try
InF:= TFileStream.Create(ParamSTR(1),fmOpenRead);
OutF := TFileStream.Create(ParamSTR(2),fmCreate);
repeat
BytesRead := InF.Read(puffer,sizeof(puffer));
inc(TotalBytesRead, BytesRead);
OutF.Write(puffer,BytesRead);
until (TotalBytesRead = InF.size);
finally
FreeAndNil(InF);
FreeAndNil(OutF);
end;
end.

Program FileCopy_Classic;
{$mode objfpc} {$H+}
var
NumRead, NumWritten : LongInt;
puffer : array [1..1048576] of byte;
InF,OutF : file of byte;
begin
assign(InF,ParamStr(1));
ReSet(InF);
Assign(OutF,ParamStr(2));
ReWrite(OutF);
repeat
BlockRead(InF,puffer,SizeOf(puffer),NumRead);
BlockWrite(OutF,puffer,NumRead,NumWritten);
until (NumRead = 0);
close(InF);
close(OutF);
end.
_______________________________________________
fpc-pascal maillist - fpc-***@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal

[Michael Van Canneyt]

Post by Géza Kovacs Géza
Hi All!
What is the faster and more efficient, using the TFileStream or the
classical way ("file of byte", or "file") type with
blockread/blockwrite and the other well-know procedures?
What is the better, faster on large files?

TFileStream offers more flexibility, but as far as efficiency is concerned :
I think that will be the same for both approaches.

For example, your first example can be done easier in a single statement:

OutF.CopyFrom(Inf,0);

Michael.

Post by Géza Kovacs Géza
See the two example code below.
Program FileCopy_stream;
{$mode objfpc} {$H+}
uses classes,SysUtils;
var
BytesRead,TotalBytesRead : Int64;
puffer : array [1..1048576] of byte;
InF, OutF : TFileStream;
begin
TotalBytesRead := 0;
BytesRead := 0;
try
InF:= TFileStream.Create(ParamSTR(1),fmOpenRead);
OutF := TFileStream.Create(ParamSTR(2),fmCreate);
repeat
BytesRead := InF.Read(puffer,sizeof(puffer));
inc(TotalBytesRead, BytesRead);
OutF.Write(puffer,BytesRead);
until (TotalBytesRead = InF.size);
finally
FreeAndNil(InF);
FreeAndNil(OutF);
end;
end.
Program FileCopy_Classic;
{$mode objfpc} {$H+}
var
NumRead, NumWritten : LongInt;
puffer : array [1..1048576] of byte;
InF,OutF : file of byte;
begin
assign(InF,ParamStr(1));
ReSet(InF);
Assign(OutF,ParamStr(2));
ReWrite(OutF);
repeat
BlockRead(InF,puffer,SizeOf(puffer),NumRead);
BlockWrite(OutF,puffer,NumRead,NumWritten);
until (NumRead = 0);
close(InF);
close(OutF);
end.
_______________________________________________
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal

[Géza Kovacs Géza]

Hi!

Thx your answer.


Can I use the "AssignFile" procedure from the SysUtils unit instead of
the simple assign procedure from the System unit?
What is the problem with the simple "assign"?

I read from the Free Pascal Wiki:
AssignFile (prevent the use of the older Assign procedure) - Assign a
name to a file

CloseFile (prevent the use of the older Close procedure) - Close opened file

What is the difference between simple "assign", "close", or
"AssignFile", and "CloseFile"?

Best regards, G
_______________________________________________
fpc-pascal maillist - fpc-***@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal

[Michael Van Canneyt]

Post by Géza Kovacs Géza
Hi!
Thx your answer.
Can I use the "AssignFile" procedure from the SysUtils unit instead of
the simple assign procedure from the System unit?
What is the problem with the simple "assign"?
AssignFile (prevent the use of the older Assign procedure) - Assign a
name to a file
CloseFile (prevent the use of the older Close procedure) - Close opened file
What is the difference between simple "assign", "close", or
"AssignFile", and "CloseFile"?

There is none, they are 100% the same.

There is no reason not to use the Assign/Close in non-gui code.

The (IMHO misguided) reason for these statements is that TPersistent and TForm (a TPersistent descendent)
have Assign and Close methods. Because of this, confusion can arise if you write Assign or Close in TForm methods.

Michael.

[Michael Schnell]

Post by Géza Kovacs Géza
Hi All!
What is the faster and more efficient, using the TFileStream or the
classical way ("file of byte", or "file") type with
blockread/blockwrite and the other well-know procedures?
What is the better, faster on large files?

As the work that needs to be done by the OS is a lot more than what is
done by the fpc library, I suppose that there is no noticeable difference.

-Michael
_______________________________________________
fpc-pascal maillist - fpc-***@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal

[Jürgen Hestermann]

As the work that needs to be done by the OS is a lot more than what is done by the fpc library, I suppose that there is no noticeable difference.

I think that depends on the size of the file(s).
If you copy thousands of files with only a few bytes each
then it may become very noticable, what "else" is done
(in additon to the pure OS copy of the files).


_______________________________________________
fpc-pascal maillist - fpc-***@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal

[Michael Schnell]

Post by Jürgen Hestermann
If you copy thousands of files with only a few bytes each
then it may become very noticable, what "else" is done
(in additon to the pure OS copy of the files).

I don't think so. Opening the file is a tedious task for the OS. So I
suppose the User-program/OS relation is not that different regarding the
file size.

-Michael
_______________________________________________
fpc-pascal maillist - fpc-***@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal

[Michael Van Canneyt]

Post by Jürgen Hestermann
If you copy thousands of files with only a few bytes each
then it may become very noticable, what "else" is done
(in additon to the pure OS copy of the files).

I don't think so. Opening the file is a tedious task for the OS. So I suppose
the User-program/OS relation is not that different regarding the file size.

Of course it is.
If you write to a file of 1Gb in blocks of 256 bytes, or you write to a 1Gb file in blocks of 1Mb,
you will surely see the difference. A kernel call always introduces overhead.

Michael.

[Jürgen Hestermann]

Post by Jürgen Hestermann
If you copy thousands of files with only a few bytes each
then it may become very noticable, what "else" is done
(in additon to the pure OS copy of the files).

I don't think so. Opening the file is a tedious task for the OS. So I suppose the User-program/OS relation is not that different regarding the file size.

I have written a file manager that logs whole disks.
When I do this twice (so that all data is already in cache on the second run)
I can log (read the meta data like name, size, date, etc.) about 50,000 files
in one second on the second run (doing this on an SSD maybe nearly as fast
on the first run already, I have never tested it).
That means it only takes 20 nanoseconds per file to read and store the meta data
which does not sound much overhead to me.

When it now comes to reading the contents of these files this may take much longer dependent on their size.
_______________________________________________
fpc-pascal maillist - fpc-***@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal