fix file related race conditions

src/main/java/com/eprosima/microxrcedds/microxrceddsgen.java

@@ -24,6 +24,7 @@
 import java.io.OutputStream;
 import java.net.URL;
 import java.util.ArrayList;
+import java.util.Comparator;
 import java.util.Vector;
 import java.util.jar.Manifest;
 
@@ -61,6 +62,7 @@ public class microxrceddsgen {
     private final String m_defaultOutputDir = "." + File.separator;
     private String m_outputDir = m_defaultOutputDir;
     private String m_tempDir = null;
+    private boolean m_tempDirCleanup = false;
     protected static String m_appName = "microxrceddsgen";
     protected boolean m_test = false;
     protected String m_defaultContainerPreallocSize = "50";
@@ -228,6 +230,13 @@ public boolean execute() {
             }
         }
 
+        if (returnedValue)
+        {
+            // be nice and clean up if no error; user may want files if there
+            // was an issue (though they have no real ability to find them...)
+            cleanUpTemp();
+        }
+
         return returnedValue;
 
     }
@@ -272,16 +281,15 @@ public static void printHelp()
     public boolean globalInit() {
         // Set the temporary folder
         if (m_tempDir == null) {
-            if (m_os.contains("Windows")) {
-                String tempPath = System.getenv("TEMP");
-
-                if (tempPath == null) {
-                    tempPath = System.getenv("TMP");
-                }
-
-                m_tempDir = tempPath;
-            } else if (m_os.contains("Linux") || m_os.contains("Mac")) {
-                m_tempDir = "/tmp/";
+            try
+            {
+                m_tempDir = java.nio.file.Files.createTempDirectory("microxrceddsgen").toString();
+                m_tempDirCleanup = true; // as we created it
+            }
+            catch (IOException e)
+            {
+                e.printStackTrace();
+                return false;
             }
         }
 
@@ -292,6 +300,36 @@ public boolean globalInit() {
         return true;
     }
 
+    private void cleanUpTemp() {
+        if (!m_tempDirCleanup) {
+            return;
+        }
+
+        try
+        {
+            // https://stackoverflow.com/a/27917071 . it's "very simple"
+            java.nio.file.Path directory = java.nio.file.Paths.get(m_tempDir);
+            java.nio.file.Files.walkFileTree(directory, new java.nio.file.SimpleFileVisitor<java.nio.file.Path>() {
+               @Override
+               public java.nio.file.FileVisitResult visitFile(java.nio.file.Path file, java.nio.file.attribute.BasicFileAttributes attrs) throws IOException {
+                   java.nio.file.Files.delete(file);
+                   return java.nio.file.FileVisitResult.CONTINUE;
+               }
+
+               @Override
+               public java.nio.file.FileVisitResult postVisitDirectory(java.nio.file.Path dir, IOException exc) throws IOException {
+                   java.nio.file.Files.delete(dir);
+                   return java.nio.file.FileVisitResult.CONTINUE;
+               }
+            });
+        }
+        catch (IOException e)
+        {
+            e.printStackTrace();
+            // we tried!
+        }
+    }
+
     private Project process(String idlFilename) {
         Project project = null;
         System.out.println("Processing the file " + idlFilename + "...");

src/main/java/com/eprosima/microxrcedds/util/Utils.java

@@ -19,6 +19,8 @@
 import com.eprosima.idl.generator.manager.TemplateST;
 
 import java.io.*;
+import java.nio.file.Files;
+import java.nio.file.Path;
 
 public class Utils
 {
@@ -88,13 +90,31 @@ public static boolean writeFile(String file, ST template, boolean replace)
         try
         {
             File handle = new File(file);
+            Path handlePath = handle.toPath();
 
             if(!handle.exists() || replace)
             {
-                FileWriter fw = new FileWriter(file);
+                // assume we might race with someone else writing the same contents
+
+                // create in same directory as output so we can do an atomic rename
+                Path temp = Files.createTempFile(handlePath.getParent(), ".microxrceddsgen", null);
+
+                FileWriter fw = new FileWriter(temp.toFile());
                 String data = template.render();
                 fw.write(data, 0, data.length());
                 fw.close();
+
+                handle.delete(); // get rid of any old file, assuming it might be outdated
+                try
+                {
+                    Files.move(temp, handlePath, java.nio.file.StandardCopyOption.ATOMIC_MOVE);
+                }
+                catch(IOException e)
+                {
+                    // assume destination exists, in which case somebody wrote
+                    // the correct contents before us, so we don't need to do
+                    // anything
+                }
             }
             else
             {