When executing the following code concurrently from many threads with a directory structure that does
not exist yet, we get "java.io.FileNotFoundException: /home/dump/129393/data/compressed/11/cost.gz
(No such file or directory)"

 File directory = new File(_directory + File.separator + Thread.currentThread().getName());
 directory.mkdirs();
 OutputStream out = new FileOutputStream(new File(directory, "cost.gz"));

This was found to be a race in Sun's J2SE code by inspection. Below, if the parent directory is created
underneath mkdirs then it never goes and makes the subdirectory:

  1144 public boolean mkdirs() {
  1145 if (exists()) {
  1146 return false;
  1147 }
  1148 if (mkdir()) {
  1149 return true;
  1150 }
  1151 File canonFile = null;
  1152 try {
  1153 canonFile = getCanonicalFile();
  1154 } catch (IOException e) {
  1155 return false;
  1156 }
  1157 String parent = canonFile.getParent();
  1158 return (parent != null) &&
  1159 (new File(parent, fs.prefixLength(parent)).mkdirs() &&
  1160 canonFile.mkdir());
  1161 }

The fix we've made is these two diffs:

==== J2SE 4: src/share/classes/java/io/File.java#2 (text) ====
@@ -1128,9 +1128,12 @@
        } catch (IOException e) {
            return false;
        }
- String parent = canonFile.getParent();
- return (parent != null) && (new File(parent).mkdirs() &&
- canonFile.mkdir());
+ File parent = canonFile.getParentFile();
+ if (parent == null) {
+ return false;
+ }
+ parent.mkdirs(); // try to make the parent directory, but ignore if somebody else beats us to the punch
+ return canonFile.mkdir();
    }
    /**
==== J2SE 5: src/share/classes/java/io/File.java#3 (text) ====
@@ -1154,10 +1154,12 @@
        } catch (IOException e) {
            return false;
        }
- String parent = canonFile.getParent();
- return (parent != null) &&
- (new File(parent, fs.prefixLength(parent)).mkdirs() &&
- canonFile.mkdir());
+ File parent = canonFile.getParentFile();
+ if (parent == null) {
+ return false;
+ }
+ parent.mkdirs(); // try to make the parent directory, but ignore if somebody else beats us to the punch
+ return canonFile.mkdir();
    }
    /**