Managing And Reporting Errors During Parallel Array Iteration In Lucee CFML 5.3.7.47

<cfscript>

	// Let's download these images in parallel.
	imageUrls = [
		"https://picsum.photos/500/300",
		"https://picsum.photos/501/301",
		"https://picsum.photos/502/302",
		"https://picsum-BAD-DNS.photos/503/303", // This will fail (invalid domain name).
		"https://picsum.photos/504/304",
		"https://picsum.photos/505/305",
		"https://picsum-BAD-DNS.photos/506/306"  // This will fail (invalid domain name).
	];

	results = withTempDirectory(
		( tempDirectory ) => {

			// Since we know that some downloads may fail (bad files, network errors,
			// server errors, etc), we're going to use a MAP instead of an EACH. This
			// way, we can create a "result" for each parallel image download operation
			// that reports the success or failure.
			var iterationResults = imageUrls.map(
				( imageUrl, i ) => {

					// For this type of "results-based" approach, I like to set up a
					// "happy path" result that can be returned AS IS; or, updated in the
					// case of an error.
					var result = {
						success: true,
						error: nullValue(),
						imageUrl: imageUrl,
						imageIndex: i,
						imageFilename: "image-#i#.jpg"
					};

					try {

						fileCopy( imageUrl, "#tempDirectory#/#result.imageFilename#" );

					} catch ( any error ) {

						// Modify the "happy path" result to represent the "sad path".
						result.success = false;
						result.error = error;

					}

					return( result );

				},
				// Parallel iteration.
				true,
				// Maximum number of threads to use.
				10
			);

			return( iterationResults );

		}
	);

	successCount = countWithProperty( results, "success", true );
	errorCount = countWithProperty( results, "success", false );

	```
	<cfoutput>
		<h1>
			Download Results
		</h1>
		<p>
			<strong>Success:</strong> #successCount#,
			<strong>Error:</strong> #errorCount#
		</p>

		<cfif errorCount>

			<p>
				The following images failed to download - re-uploading the images may
				fix some of these errors.
			</p>
			<ul>
				<cfloop value="result" array="#results#">
					<cfif ! result.success>
						<li>
							#encodeForHtml( result.imageUrl )#
						</li>
					</cfif>
				</cfloop>
			</ul>

		</cfif>
	</cfoutput>
	```

	// ------------------------------------------------------------------------------- //
	// ------------------------------------------------------------------------------- //

	/**
	* I create a temp directory and pass it to the given operator. Any value returned
	* from the operator is automatically passed back to the calling context. The temp
	* directory is deleted once the operator finishes executing.
	*/
	public any function withTempDirectory( required function operator ) {

		var path = expandPath( "./temp-#createUniqueId()#" );

		directoryCreate( path );

		try {

			return( operator( path ) );

		} finally {

			// NOTE: Normally I would delete all the temp directory stuff once I was done
			// with it; however, for the demo, I'm going to keep this around.
			// --
			// directoryDelete( path, true );

		}

	}


	/**
	* I count the number of items that have the given key-value pair.
	*/
	public numeric function countWithProperty(
		required array collection,
		required string key,
		required any value
		) {

		var count = 0;

		for ( var item in collection ) {

			if ( item[ key ] == value ) {

				count++;

			}

		}

		return( count );

	}

</cfscript>