Improve performance by dividing up tasks

The stream of inkscape commands have been divided across multiple
instances of inkscape, one per core. This speeds up rendering by
using more cpu cores, even for single svg rendering. To do this a
simple java program was written which starts N instances of
whatever arguments was passed to it and then reads one line at the
time from standard input, the lines are then divided into N
seperate streams which are then piped to the the difference instances
of whatever program was passed as argument to SplitJob.

src/SplitJob.java

@@ -0,0 +1,54 @@
+
+import java.io.*;
+
+import static java.lang.ProcessBuilder.Redirect;
+
+public class SplitJob {
+
+	private static final BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
+
+
+	public static void main(String[] args) {
+
+		final Runtime runtime = Runtime.getRuntime();
+		int numThreads = runtime.availableProcessors();
+		Process[] procs = new Process[numThreads];
+
+		try {
+		
+			ProcessBuilder builder = new ProcessBuilder(args);
+			builder.redirectError(Redirect.INHERIT);
+		
+			for (int i = 0; i < numThreads; i++) {
+				procs[i] = builder.start();
+			}
+		
+			for (int i = 0; ; i = (i + 1) % numThreads) {
+	
+				String s = in.readLine();
+
+				if (s == null)
+					break;
+
+				byte[] data = (s + '\n').getBytes();
+				procs[i].getOutputStream().write(data, 0, data.length);
+				procs[i].getOutputStream().flush();
+			}
+		
+			for (Process proc : procs) {
+			
+				proc.getOutputStream().close();
+				int exitCode = proc.waitFor();
+				
+				if (exitCode != 0) {
+					System.err.printf("[Error] %s stopped with exit code: %d\n", args[0], exitCode);
+					System.exit(2);
+				}
+			}
+			
+		} catch (Exception e) {
+			System.err.printf("[Error] %s: %s\n", e.getClass().getName(), e.getMessage());
+			System.exit(1);
+		}
+	}
+}

src/render_icons.sh

@@ -68,13 +68,12 @@ do
     # since we finished rendering it out last.
     if [[ $CONTEXT.svg -nt .${CONTEXT}_timestamp ]]
     then
-        genInkscapeCmds $CONTEXT | $INKSCAPE --shell > /dev/null && touch .${CONTEXT}_timestamp &
+        echo "Rendering icons from $CONTEXT.svg"
+        genInkscapeCmds $CONTEXT | java SplitJob $INKSCAPE --shell && touch .${CONTEXT}_timestamp
     else
         echo "No changes to $CONTEXT.svg, skipping..."
     fi
 done
 
-wait
-
 # Remove all empty directories from the theme folder.
 find $THEMEDIR -type d -empty -delete