Fixed possible thread blocking issue

app/press/Compressor.java

@@ -278,11 +278,29 @@ protected static VirtualFile getCompressedFile(FileCompressor compressor,
             }
         }
 
+        //
+        // We create a temp file to which the output will be written to first,
+        // and then rename it to the target file name (because compression can
+        // take a while)
+        // If the temp file is already being written by another thread, this
+        // method will block until it is complete and then return null
+        //
+        File tmp = getTmpOutputFile(file);
+        if (tmp == null) {
+            PressLogger.trace("Compressed file was generated by another thread");
+        } else {
+            writeCompressedFile(compressor, componentFiles, file, tmp);
+        }
+
+        return file;
+    }
+
+    private static void writeCompressedFile(FileCompressor compressor,
+            List<FileInfo> componentFiles, VirtualFile file, File tmp) {
         Writer out = null;
         try {
-            // Compress the component files and write the output to a temporary
-            // file
-            File tmp = createTempFile(file);
+            // Compress the component files and write the output to the
+            // temporary file
             out = new BufferedWriter(new FileWriter(tmp));
 
             // Add the last modified dates of each component file to the start
@@ -300,7 +318,7 @@ protected static VirtualFile getCompressedFile(FileCompressor compressor,
                     .getRealFile().getName(), (timeAfter - timeStart));
 
             // Once the compressed output has been written to the temporary
-            // file, move it to the cache directory.
+            // file, rename it to overwrite the original file.
             String msg = "Output written to temporary file\n%s\n";
             msg += "Moving from tmp path to final path:\n%s";
             String tmpPath = tmp.getAbsolutePath();
@@ -326,8 +344,46 @@ protected static VirtualFile getCompressedFile(FileCompressor compressor,
                 }
             }
         }
+    }
 
-        return file;
+    private static File getTmpOutputFile(VirtualFile file) {
+        String origPath = file.getRealFile().getAbsolutePath();
+        File tmp = new File(origPath + ".tmp");
+
+        // If the temp file already exists
+        if (tmp.exists()) {
+            long tmpLastModified = tmp.lastModified();
+            long now = System.currentTimeMillis();
+
+            // If the temp file is older than the destination file, or if it is
+            // older than the allowed compression time, it must be a remnant of
+            // a previous server crash so we can overwrite it
+            if (tmpLastModified < file.lastModified()) {
+                return tmp;
+            }
+            if (now - tmpLastModified > PluginConfig.maxCompressionTimeMillis) {
+                return tmp;
+            }
+
+            // Otherwise it must be currently being written by another thread,
+            // so wait for it to finish
+            while (tmp.exists()) {
+                if (System.currentTimeMillis() - now > PluginConfig.maxCompressionTimeMillis) {
+                    throw new PressException("Timeout waiting for compressed file to be generated");
+                }
+
+                try {
+                    Thread.sleep(1000);
+                } catch (InterruptedException e) {
+                }
+            }
+
+            // Return null to indicate that the file was already generated by
+            // another thread
+            return null;
+        }
+
+        return tmp;
     }
 
     public static List<File> clearCache(String compressedDir, String extension) {
@@ -554,20 +610,6 @@ private static VirtualFile getVirtualFile(String filePath) {
         return VirtualFile.open(Play.getFile(filePath));
     }
 
-    /**
-     * Creates a temporary version of a file that will later be copied over the
-     * original
-     */
-    private static File createTempFile(VirtualFile original) {
-        String origPath = original.getRealFile().getAbsolutePath();
-        File tmpFile = new File(origPath + ".tmp");
-        for (int i = 1; tmpFile.exists(); i++) {
-            tmpFile = new File(origPath + ".tmp");
-        }
-
-        return tmpFile;
-    }
-
     protected static class FileInfo {
         String fileName;
         boolean compress;

app/press/PluginConfig.java

@@ -25,6 +25,10 @@ public static class DefaultConfig {
         // less than a second)
         public static final String compressionKeyStorageTime = "2mn";
 
+        // The maximum amount of time in milli-seconds allowed for compression
+        // to occur before a timeout exception is thrown.
+        public static final int maxCompressionTimeMillis = 60000;
+
         public static class js {
             // The directory where source javascript files are read from
             public static final String srcDir = "/public/javascripts/";
@@ -56,6 +60,7 @@ public static class css {
     public static CachingStrategy cache;
     public static boolean cacheClearEnabled;
     public static String compressionKeyStorageTime;
+    public static int maxCompressionTimeMillis;
 
     public static class js {
         public static String srcDir = DefaultConfig.js.srcDir;
@@ -90,6 +95,8 @@ public static void readConfig() {
         enabled = ConfigHelper.getBoolean("press.enabled", DefaultConfig.enabled);
         compressionKeyStorageTime = ConfigHelper.getString("press.key.lifetime",
                 DefaultConfig.compressionKeyStorageTime);
+        maxCompressionTimeMillis = ConfigHelper.getInt("press.compression.maxTimeMillis",
+                DefaultConfig.maxCompressionTimeMillis);
 
         css.srcDir = ConfigHelper.getString("press.css.sourceDir", DefaultConfig.css.srcDir);
         css.compressedDir = ConfigHelper.getString("press.css.outputDir",

documentation/manual/home.textile

@@ -148,6 +148,12 @@ When the **#{press.compressed-script}** or **#{press.compressed-stylesheet}** ta
 **press.key.lifetime=2mn**
 
 
+h3. __press.compression.maxTimeMillis__
+
+The maximum amount of time in milli-seconds that compression is allowed to take before a timeout exception is thrown.
+**press.compression.maxTimeMillis=60000**
+
+
 h3. __press.js.sourceDir__
 
 The source directory for javascript files, relative to the application root