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Visual Basic 6.0 Examples

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(Visual Basic 6.0) Chaining Asynchronous Streams

The asynchronous functionality of Chilkat, combined with streams, can offer some interesting possibilities. This example demonstrates how to create two streams, call them streamA and streamB, where streamA feeds into streamB and both streams run in background threads. The examples demonstrates copying a file in this way:

sourceFile --> streamA --> streamB --> outputFile

This may seem pointless, but the possibilities become interesting when intermediate streams can perform tasks such as encryption or compression, or when a source or sink is a socket, a TLS connection, an SSH tunnel, etc. Or perhaps if a stream becomes the source for the file in an HTTP upload, or perhaps it is the source or sink for files in FTP, SFTP, etc. This is where Chilkat's Async standards in combination with Chilkat Stream can begin to offer powerful and simple-to-implement possibilities.

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

Dim streamA As New ChilkatStream
Dim streamB As New ChilkatStream

streamA.SourceFile = "qa_data/hamlet.xml"

'  streamA will feed into streamB. (streamA is the source for streamB)
Dim success As Long
success = streamB.SetSourceStream(streamA)

streamB.SinkFile = "qa_output/hamlet_copy.xml"

'  Run each stream asynchronously in background threads:
Dim taskA As ChilkatTask
Set taskA = streamA.RunStreamAsync()
Dim taskB As ChilkatTask
Set taskB = streamB.RunStreamAsync()

'  Start each task. (The call to Run returns immediately.
'  each task begins running in its own background thread.)
success = taskA.Run()
success = taskB.Run()

'  Wait for each task to complete.
'  Note: The SleepMs method is a utility method that puts the caller to sleep
'  for a specified number of milliseconds.
'  It is the caller's thread that sleeps (i.e. this foreground thread).
'  It does not cause the background thread of the given task object to sleep.
Do While ((taskA.Finished <> 1) Or (taskB.Finished <> 1))
    taskB.SleepMs 20
Loop

'  At this point, each background task has finished.
'  Let's check to see if each stream succeeded.

'  Did streamA succeed in reading the entire file?
If (taskA.TaskSuccess <> 1) Then
    Debug.Print "streamA failed:"
    Debug.Print taskA.ResultErrorText
    success = 0
End If

'  Did streamB succeed in writing the entire file?
If (taskB.TaskSuccess <> 1) Then
    Debug.Print "streamB failed:"
    Debug.Print taskB.ResultErrorText
    success = 0
End If

If (success <> 1) Then
    Exit Sub
End If

'  Let's double-check to see that the files are equal in size and content:
Dim fac As New CkFileAccess

Dim bFilesEqual As Long
bFilesEqual = fac.FileContentsEqual(streamA.SourceFile,streamB.SinkFile)
If (bFilesEqual <> 1) Then
    Debug.Print "The output file is not equal to the input file!"
Else
    Debug.Print "The file was successfully copied in a very roundabout way!"
End If


 

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