Read process output on separate thread

If the process's output stream isn't read from, the buffer will get too
full and the process will block. Thus our process.waitFor call will
never finish. We need to instead read the process output in parallel as
we wait for the process to finish.

Author: hinerm

src/main/java/net/imagej/ui/swing/updater/LauncherMigrator.java

@@ -533,15 +533,25 @@ private static void extractAndSetProperty(
 	private static List<String> collectProcessOutput(Process p)
 		throws IOException, InterruptedException
 	{
+		List<String> outputLines = new ArrayList<>();
+		Thread outputReader = new Thread(() -> {
+			try (BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()))) {
+				String line;
+				while ((line = reader.readLine()) != null) {
+					outputLines.add(line);
+				}
+			} catch (IOException e) {
+				e.printStackTrace();
+			}
+		});
+
+		outputReader.start();
 		boolean completed = p.waitFor(5, TimeUnit.SECONDS);
 		if (!completed) {
 			p.destroyForcibly();
 			throw new IOException("Process took too long to complete.");
 		}
-		p.exitValue();
-		try (BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()))) {
-			return reader.lines().collect(Collectors.toList());
-		}
+		return outputLines;
 	}
 
 	/** Annoying code to discern the AWT/Swing main application frame, if any. */