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(VB.NET) 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.
Dim streamA As New Chilkat.Stream Dim streamB As New Chilkat.Stream streamA.SourceFile = "qa_data/hamlet.xml" ' streamA will feed into streamB. (streamA is the source for streamB) Dim success As Boolean = streamB.SetSourceStream(streamA) streamB.SinkFile = "qa_output/hamlet_copy.xml" ' Run each stream asynchronously in background threads: Dim taskA As Chilkat.Task = streamA.RunStreamAsync() Dim taskB As Chilkat.Task = 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. While ((taskA.Finished <> True) Or (taskB.Finished <> True)) taskB.SleepMs(20) End While ' 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 <> True) Then Console.WriteLine("streamA failed:") Console.WriteLine(taskA.ResultErrorText) success = False End If ' Did streamB succeed in writing the entire file? If (taskB.TaskSuccess <> True) Then Console.WriteLine("streamB failed:") Console.WriteLine(taskB.ResultErrorText) success = False End If If (success <> True) Then Exit Sub End If ' Let's double-check to see that the files are equal in size and content: Dim fac As New Chilkat.FileAccess Dim bFilesEqual As Boolean = fac.FileContentsEqual(streamA.SourceFile,streamB.SinkFile) If (bFilesEqual <> True) Then Console.WriteLine("The output file is not equal to the input file!") Else Console.WriteLine("The file was successfully copied in a very roundabout way!") End If
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