[kylin] branch master updated: KYLIN-3617 Add javadoc for magic number in isTaskExecutableOutput

[sh...@apache.org]

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shaofengshi pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/kylin.git


The following commit(s) were added to refs/heads/master by this push:
     new 2de2b9f  KYLIN-3617 Add javadoc for magic number in isTaskExecutableOutput
2de2b9f is described below

commit 2de2b9fced1ba27b1688b803e119160aa45950fc
Author: hit-lacus <hi...@126.com>
AuthorDate: Sun Dec 9 21:23:17 2018 +0800

    KYLIN-3617 Add javadoc for magic number in isTaskExecutableOutput
---
 .../org/apache/kylin/job/dao/ExecutableDao.java    | 25 +++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java b/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java
index 4e7188a..a4dc4c1 100644
--- a/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java
+++ b/core-job/src/main/java/org/apache/kylin/job/dao/ExecutableDao.java
@@ -31,6 +31,8 @@ import org.apache.kylin.common.persistence.ResourceStore;
 import org.apache.kylin.common.persistence.Serializer;
 import org.apache.kylin.common.util.AutoReadWriteLock;
 import org.apache.kylin.job.exception.PersistentException;
+import org.apache.kylin.job.execution.AbstractExecutable;
+import org.apache.kylin.job.execution.DefaultChainedExecutable;
 import org.apache.kylin.metadata.cachesync.Broadcaster;
 import org.apache.kylin.metadata.cachesync.CachedCrudAssist;
 import org.apache.kylin.metadata.cachesync.CaseInsensitiveStringCache;
@@ -164,8 +166,29 @@ public class ExecutableDao {
         Broadcaster.getInstance(config).registerListener(new JobOutputSyncListener(), "execute_output");
     }
 
+    /**
+     * Length of java.util.UUID's string representation is always 36.
+     */
+    private static final int UUID_STRING_REPRESENTATION_LENGTH = 36;
+
+    /**
+     * <pre>
+     *    Backgroud :
+     * 1. Each Executable has id, and id should be unique, we use java.util.UUID to create id of Executable.
+     * 2. 36(UUID_STRING_REPRESENTATION_LENGTH) is a magic number, and it is the length of string of java.util.UUID.toString(). It can verified this simply by `System.out.println(UUID.randomUUID().toString().length());`
+     * 3. All subtask of a ChainedExecutable is also a Executable, its id is a string which length is 39 (36 + 3). See DefaultChainedExecutable#addTask.
+     * 4. Any other Executable's id is a String created by UUID.toString(), so its length is 36.
+     * 5. This method may be a bit fragile/confusing because it depend on specific implementation of subclass of Executable.
+     * </pre>
+     *
+     * @see DefaultChainedExecutable#addTask(AbstractExecutable)
+     * @see AbstractExecutable#AbstractExecutable()
+     *
+     * @param id id of a Executable (mostly it is a UUID)
+     * @return true if the job is a subtask of a ChainedExecutable; else return false
+     */
     private boolean isTaskExecutableOutput(String id) {
-        return id.length() > 36;
+        return id.length() > UUID_STRING_REPRESENTATION_LENGTH;
     }
 
     private class JobSyncListener extends Broadcaster.Listener {