Indy TIdHTTPServer and safe multithread behavior
lazarus / 38-Networking and Web Programming

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hrayon · 2017-02-15 17:37

I want to increment the value of a global variable securely, but the
increment routine is within the OnCommandGet method of the object of
type TIdHTTPServer. The correct way would be to use the
TCriticalSection variable?
See the pseudo-code:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
...g_TCriticalSection_Flag: TCriticalSection;g_integer_counter:
Integer;...On Start Daemon   g_TCriticalSection_Flag: =
TCriticalSection.Create;   g_integer_counter: = 0;End On Start
Daemon OnCommandGet   Try      g_TCriticalSection_Flag.Enter;     
g_integer_counter: = g_integer_counter + 1;   Finally     
g_TCriticalSection_Flag.Leave;   EndEnd OnCommandGet On Stop Daemon  
g_TCriticalSection_Flag.Free;End On Stop Daemon

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Remy Lebeau · 2017-02-22 03:27

Quote from: hrayon on February 15, 2017, 06:37:20 pmI want to
increment the value of a global variable securely, but the increment
routine is within the OnCommandGet method of the object of type
TIdHTTPServer. The correct way would be to use the TCriticalSection
variable?

That is one way to do it.  And Indy even have a TIdThreadSafeInteger
class for that very purpose:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses  ...,
IdThreadSafe; g_integer_counter: TIdThreadSafeInteger; On Start
Daemon   g_integer_counter := TIdThreadSafeInteger.Create;End On Start
Daemon OnCommandGet  g_integer_counter.Increment;End OnCommandGet On
Stop Daemon  g_integer_counter.Free;End On Stop Daemon 
On the other hand, if you don't want the overhead of a critical
section, you can use atomic APIs instead, like
System.InterlockedIncrement():

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
g_integer_counter: Longint; On Start Daemon   g_integer_counter :=
0;End On Start Daemon OnCommandGet 
InterLockedIncrement(g_integer_counter);End OnCommandGet