Here if/then constructs are not robust because changes can happen in between. When working with files this is typically done in a situation where producers and consumers work concurrently. Robust File Operationsįor file operations one should consider using those from the Microsoft.VisualBasic namespace because they are more robust than those in System.IO and offer more features like automatically overwriting existing files. The FSW minimizes usage of precious non-paged memory via its InternalBufferSize property and throws an InternalBufferOverflowException „Too many changes at once in directory …“when exceeded. Maybe not discovering the need to implement an OnError handler and being misled by the FSW throwing exception until started is the reason for the wrongly perceived bad reliability of the FSW. Strangely this so important FSW Error event does not show up in the Win Forms designer, my wrappers fix this. To prevent exceptions going unnoticed one must handle the Error event. This is typical for the Event-based Asynchronous Pattern (EAP). While watching for changes the FSW reports exceptions via its Error event only and does does not raise them.
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The FSW only throws exceptions on problems when setting its properties. An easy way to create lots of files and file system events is repeatedly copying and pasting all files in a directory via CTRL+A, CTRL-C, CTRL-V. Your watcher now only needs to watch for a single renamed event per file. NET applications a file rename is an atomic operation. If you have control over the file producer you can easily tame this event flood by renaming the files to the watched directory or watched extension only when they are totally complete. xlsx file and triggers 8 events for 3 different files of which none is changed event for the file changed one would naively expect:įile system event flood triggered by Excel for single actions like „Save“ Ex: Excel triggers 15 NTFS events for 4 different files when creating a single new. Some applications trigger lots of file system events for a single action.
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Does automatically handle renames of its watch path.Does detect network disruptions, but does not automatically recover from them.Does not report files that existed before.Reports exceptions via its Error event.No option to report files existing before the FSW started.
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However, there are typical problems one may encounter when first using the FSW: If used properly the standard FileSystemWatcher (FSW) is way better than its reputation.
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For tips about handling lots of files and using contig.exe to defragment NTFS indexes see NTFS performance and large volumes of files and directories. They allow you to easily process files without having to spawn a Thread or create a Task yourself and allow to configure the degree of parallelism desired. To process files detected in either way I recommend using TPL DataFlow ActionBlocks. For a file system watcher using polling instead of file system events see my FilePoller. Use my RecoveringFileSystemWatcherto automatically recover from typical transient watch path accessibility problems. Param ( # Use Generate Session URL function to obtain a value for -sessionUrl parameter.Simply replace the standard FSW with my BufferingFileSystemWatcherand you no longer need to worry about InternalBufferOverflowExceptions.