Category: Delphi RAD Studio Article

What is Memory Leak

A memory leak is a kind of resource consumption that occurs when the code does not manage memory allocations while creating the objects. So in order to manage it, the memory used by the object created should be released when not needed. For example, if you call a function or procedure where the object is created and not released then it goes on consuming memories due to multiple calls from the calling programme. A memory leak may also happen when an object is stored in memory but cannot be accessed by the running code.

This could be a serious issue when the system or service is used for 24x7x365 without addressing it. If not handled it will slow down the system by consuming all resources and finally hangs the system.

How to solve it

There are several third party tools available but the simple solution solution is to release or free the used components or objects when not needed while exiting the funtion procedure.

Example:

procedure DoSomething;
var sl : TStringList;
begin
  sl := TStringList.create()
  try
    try
      // code that may raise exception
      sl.Add('suren');
      sl.Add('sujan');
    except
      ShowMessage('Error occured !');
    end;
  finally
    // Free all memory used in this block
    sl.free;
  end;
end;

Note that there are two try blocks are used in above code. They are different and serve two different purposes. First try is used to make all objects free and the second try is used to trap the errors.

The finally block will always be executed, even if there is no exception, while the except block is only executed when there is an exception.

The finally block is even executed when you exit the function early using Exit in a try-finally block.

The except block is meant to handle the exception(s), while the finally block is not. The finally block is meant to contain code that should be executed regardless of an exception, i.e. mainly to protect resources. That is why you should do:

s := b.Create;
try
  // Code that may raise an exception.
finally
  s.Free; // Free resource, even if there was an exception.
          // Exception is NOT handled.
end;

and:

try
  // Code that may raise an exception.
except
  // Handle the kind of exceptions you can handle.
end;

combined :

try
  try
    // code that may raise exception
  except
    // Handle Exception;
  end;
finally
    // Free all memory used in this block
end;

Note the finally block is not limited to memory management. It can be used for other actions like restoring/undo/close opened files, close open connections, shut down hardware that was started etc.

While installing Windows Services, you may get “System error 5 has occurred”  Error or “EOSError Code: 5 Access Denied” Error. This error was due to insufficient permission to run command. The easiest way to run Command Prompt as an administrator is to find the “command prompt” in Search and once you find it, right-click on the “Command Prompt” and then Choose “Run as administrator” to run it with administrative privileges.

Another option is to run in command prompt as below:

C:\net user administrator /active:yes

It is also possible to run netplwiz to solve this error

Windows Service Application

What is Windows Service?

Microsoft Windows service is an application software which runs in the background. Service applications accept requests from client applications, process those requests, and return information to the client applications. As it runs in the background, it does not require user input interaction. These services can be automatically started when the computer boots, can be paused and restarted, and do not show any user interface. The service can have multiple methods to execute at the background level. So it can be used for different background processing like checking system update, processing routines, validations of data etc.

Why do we need it?

Windows services are needed when an application needs to continuously run without user interaction. Services runs until it is stopped or the computer is turned off. When the system needs to respond 24/7/365, then Windows Services Applications are used. When it is running, it is capable of getting requests from clients and return the response.

What are its limitations?

Service Application does not allow to use visual components. Only non-visual components are allowed in service applications. Besides that every processing in the background can be achieved.

When there is a requirement of huge data communication between client and server, DataSnap will be the right choice as it is more flexible and can be deployed as Windows services and Web Services usiing IIS, Apachy and even standalone server.