What does 'sleep' function do?

[winterslam]

With reference to my previous thread on copying USB drive



http://www.vbforums.com/showthread.php?t=503894

Private Declare Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)

I was told that the 'sleep' function pauses the application for specified time interval. (May not necessarily give time to other processes to run simultaneously ).

Is it true?


So what is the difference between 'sleep' and this loop?

Dim date1 As Date
date1 = Now
While (DateDiff("s", date1, Now) < 5)
Wend

My main concern is to let my application give some breathing time to other processes while copying folders of several gig in size

[RobDog888]

Sleep will tstop the processing on your thread. While that loop will "simulate " sleep but it will also lock up the thread from processing but not if you place a DoEvents in it.

[Merri]

So basically Sleep is what gives the processing time to everything else that is running, as your process is halted and not processed until the specified time has passed.

DoEvents causes message queue to be processed, thus the result it gives within a heavy loop is that your application's windows get drawn, mouse and keyboard messages are triggered if there are any in the queue etc. - thus preventing your application from getting a locked up feeling.


If you have a window open, you don't want to sleep too long. You may catch a cold... err... I mean, your application gets unresponsive. So you probably want to create a loop that first calls Sleep for a little while, then calls for DoEvents to make sure your windows are drawn etc. and then just go back to Sleep again, all the way until you know your other processing is done.

[winterslam]

Below is my code. The application runs in background. No Form..

The function copies the source folder to the destination folder.

I don't mind if the program takes 1 hour to copy a folder instead of 10 minutes as long as it gives time to other processes on the system




Is the placement of DoEvents correct?

Option Explicit
Private Declare Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)
Dim fso As New FileSystemObject


Public Sub FolderCopy(ByVal source As String, ByVal destination As String)
          Dim objfile As File
          Dim objfolder As Folder       
                 
                 
          DoEvents
              
          For Each objfile In fso.GetFolder(source).Files
                  DoEvents
                  
                  On Error Resume Next
                  If objfile.Name <> "" Then
                        objfile.Copy destination & "\" & objfile.Name, True
                        Sleep 100
                  End If
                 

         Next
         For Each objfolder In fso.GetFolder(source).SubFolders
                        DoEvents
                        On Error Resume Next
                        If Dir(destination & "\" & objfolder.Name) = "" Then MkDir destination & "\" & objfolder.Name
                        FolderCopy objfolder.Path, destination & "\" & objfolder.Name
    
         Next      
      

End Sub

[Merri]

If you have no form then using DoEvents doesn't serve you any purpose. DoEvents only handles messages of your application.

[RobDog888]

The Sleep function suspends the execution of the current thread for a specified interval.

· dwMilliseconds
Specifies the time, in milliseconds, for which to suspend execution. A value of zero causes the thread to relinquish the remainder of its time slice to any other thread of equal priority that is ready to run. If there are no other threads of equal priority ready to run, the function returns immediately, and the thread continues execution. A value of INFINITE causes an infinite delay.

The SleepEx function causes the current thread to enter a wait state until one of the following occurs:· An I/O completion callback function is called· An asynchronous procedure call (APC) is queued to the thread.· The time-out interval elapses

· dwMilliseconds
Specifies the time, in milliseconds, that the delay is to occur. A value of zero causes the function to return immediately. A value of INFINITE causes an infinite delay.

· bAlertable
Specifies whether the function may terminate early due to an I/O completion callback function or an APC. If bAlertable is FALSE, the function does not return until the time-out period has elapsed. If an I/O completion callback occurs, the function does not return and the I/O completion function is not executed. If an APC is queued to the thread, the function does not return and the APC function is not executed.
If bAlertable is TRUE and the thread that called this function is the same thread that called the extended I/O function (ReadFileEx or WriteFileEx), the function returns when either the time-out period has elapsed or when an I/O completion callback function occurs. If an I/O completion callback occurs, the I/O completion function is called. If an APC is queued to the thread (QueueUserAPC), the function returns when either the timer-out period has elapsed or when the APC function is called.

Maybe these will help clear things up.[/color]

[MartinLiss]

... DoEvents only handles messages of your application.

It handles all Windows messages. From Help:

DoEvents switches control to the operating-environment kernel. Control returns to your application as soon as all other applications in the environment have had a chance to respond to pending events. This doesn't cause the current application to give up the focus, but it does enable background events to be processed.

[winterslam]

final question..


Is the 'sleep' keyword in my code necessary at all?

[RobDog888]

No its not but if you use the File Operations APIs to use the build in Windows File Copy process and show a dialog with a progressbar it should give the duration / progress of the copy at least.