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(PowerBuilder) 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.
integer li_rc oleobject loo_StreamA oleobject loo_StreamB integer li_Success oleobject loo_TaskA oleobject loo_TaskB oleobject loo_Fac integer li_BFilesEqual loo_StreamA = create oleobject li_rc = loo_StreamA.ConnectToNewObject("Chilkat_9_5_0.Stream") if li_rc < 0 then destroy loo_StreamA MessageBox("Error","Connecting to COM object failed") return end if loo_StreamB = create oleobject li_rc = loo_StreamB.ConnectToNewObject("Chilkat_9_5_0.Stream") loo_StreamA.SourceFile = "qa_data/hamlet.xml" // streamA will feed into streamB. (streamA is the source for streamB) li_Success = loo_StreamB.SetSourceStream(loo_StreamA) loo_StreamB.SinkFile = "qa_output/hamlet_copy.xml" // Run each stream asynchronously in background threads: loo_TaskA = loo_StreamA.RunStreamAsync() loo_TaskB = loo_StreamB.RunStreamAsync() // Start each task. (The call to Run returns immediately. // each task begins running in its own background thread.) li_Success = loo_TaskA.Run() li_Success = loo_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 ((loo_TaskA.Finished <> 1) OR (loo_TaskB.Finished <> 1)) loo_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 loo_TaskA.TaskSuccess <> 1 then Write-Debug "streamA failed:" Write-Debug loo_TaskA.ResultErrorText li_Success = 0 end if // Did streamB succeed in writing the entire file? if loo_TaskB.TaskSuccess <> 1 then Write-Debug "streamB failed:" Write-Debug loo_TaskB.ResultErrorText li_Success = 0 end if if li_Success <> 1 then destroy loo_StreamA destroy loo_StreamB return end if // Let's double-check to see that the files are equal in size and content: loo_Fac = create oleobject li_rc = loo_Fac.ConnectToNewObject("Chilkat_9_5_0.FileAccess") li_BFilesEqual = loo_Fac.FileContentsEqual(loo_StreamA.SourceFile,loo_StreamB.SinkFile) if li_BFilesEqual <> 1 then Write-Debug "The output file is not equal to the input file!" else Write-Debug "The file was successfully copied in a very roundabout way!" end if destroy loo_StreamA destroy loo_StreamB destroy loo_Fac
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