HADOOP-12009. Clarify FileSystem.listStatus() sorting order & fix FileSystemContractBaseTest:testListStatus. backport to 2.8

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileSystem.java

@@ -1520,7 +1520,9 @@ public abstract class FileSystem extends Configured implements Closeable {
   /**
    * List the statuses of the files/directories in the given path if the path is
    * a directory.
-   * 
+   * <p>
+   * Does not guarantee to return the List of files/directories status in a
+   * sorted order.
    * @param f given path
    * @return the statuses of the files/directories in the given patch
    * @throws FileNotFoundException when the path does not exist;
@@ -1562,6 +1564,9 @@ public abstract class FileSystem extends Configured implements Closeable {
   /**
    * Filter files/directories in the given path using the user-supplied path
    * filter.
+   * <p>
+   * Does not guarantee to return the List of files/directories status in a
+   * sorted order.
    * 
    * @param f
    *          a path name
@@ -1582,6 +1587,9 @@ public abstract class FileSystem extends Configured implements Closeable {
   /**
    * Filter files/directories in the given list of paths using default
    * path filter.
+   * <p>
+   * Does not guarantee to return the List of files/directories status in a
+   * sorted order.
    * 
    * @param files
    *          a list of paths
@@ -1598,6 +1606,9 @@ public abstract class FileSystem extends Configured implements Closeable {
   /**
    * Filter files/directories in the given list of paths using user-supplied
    * path filter.
+   * <p>
+   * Does not guarantee to return the List of files/directories status in a
+   * sorted order.
    * 
    * @param files
    *          a list of paths
@@ -1761,6 +1772,8 @@ public abstract class FileSystem extends Configured implements Closeable {
    * while consuming the entries. Each file system implementation should
    * override this method and provide a more efficient implementation, if
    * possible. 
+   * Does not guarantee to return the iterator that traverses statuses
+   * of the files in a sorted order.
    *
    * @param p target path
    * @return remote iterator
@@ -1788,6 +1801,8 @@ public abstract class FileSystem extends Configured implements Closeable {
 
   /**
    * List the statuses and block locations of the files in the given path.
+   * Does not guarantee to return the iterator that traverses statuses
+   * of the files in a sorted order.
    * 
    * If the path is a directory, 
    *   if recursive is false, returns files in the directory;

hadoop-common-project/hadoop-common/src/site/markdown/filesystem/filesystem.md

@@ -152,6 +152,10 @@ to the same path:
     forall fs in listStatus(Path) :
       fs == getFileStatus(fs.path)
 
+**Ordering of results**: there is no guarantee of ordering of the listed entries.
+While HDFS currently returns an alphanumerically sorted list, neither the Posix `readdir()`
+nor Java's `File.listFiles()` API calls define any ordering of returned values. Applications
+which require a uniform sort order on the results must perform the sorting themselves.
 
 #### Atomicity and Consistency
 

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/FileSystemContractBaseTest.java

@@ -20,6 +20,7 @@ package org.apache.hadoop.fs;
 
 import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.util.ArrayList;
 
 import junit.framework.TestCase;
 
@@ -203,9 +204,13 @@ public abstract class FileSystemContractBaseTest extends TestCase {
 
     paths = fs.listStatus(path("/test/hadoop"));
     assertEquals(3, paths.length);
-    assertEquals(path("/test/hadoop/a"), paths[0].getPath());
-    assertEquals(path("/test/hadoop/b"), paths[1].getPath());
-    assertEquals(path("/test/hadoop/c"), paths[2].getPath());
+    ArrayList<Path> list = new ArrayList<Path>();
+    for (FileStatus fileState : paths) {
+      list.add(fileState.getPath());
+    }
+    assertTrue(list.contains(path("/test/hadoop/a")));
+    assertTrue(list.contains(path("/test/hadoop/b")));
+    assertTrue(list.contains(path("/test/hadoop/c")));
 
     paths = fs.listStatus(path("/test/hadoop/a"));
     assertEquals(0, paths.length);