[jira] [Commented] (HADOOP-18740) s3a prefetch cache blocks should be accessed by RW locks

[ASF GitHub Bot (Jira)]

    [ 
https://issues.apache.org/jira/browse/HADOOP-18740?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17727999#comment-17727999
 ] 

ASF GitHub Bot commented on HADOOP-18740:
-----------------------------------------

steveloughran commented on code in PR #5675:
URL: https://github.com/apache/hadoop/pull/5675#discussion_r1211811893


##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/SingleFilePerBlockCache.java:
##########
@@ -99,6 +106,32 @@ public String toString() {
           "([%03d] %s: size = %d, checksum = %d)",
           blockNumber, path, size, checksum);
     }
+
+    /**
+     * Take the read or write lock.
+     *
+     * @param lockType type of the lock.
+     */
+    void takeLock(LockType lockType) {
+      if (LockType.READ == lockType) {
+        this.lock.readLock().lock();

Review Comment:
   remove the `this.`



##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/SingleFilePerBlockCache.java:
##########
@@ -99,6 +106,32 @@ public String toString() {
           "([%03d] %s: size = %d, checksum = %d)",
           blockNumber, path, size, checksum);
     }
+
+    /**
+     * Take the read or write lock.
+     *
+     * @param lockType type of the lock.
+     */
+    void takeLock(LockType lockType) {
+      if (LockType.READ == lockType) {
+        this.lock.readLock().lock();
+      } else if (LockType.WRITE == lockType) {
+        this.lock.writeLock().lock();
+      }
+    }
+
+    /**
+     * Release the read or write lock.
+     *
+     * @param lockType type of the lock.
+     */
+    void releaseLock(LockType lockType) {
+      if (LockType.READ == lockType) {
+        this.lock.readLock().unlock();

Review Comment:
   remove the `this.`



##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/SingleFilePerBlockCache.java:
##########
@@ -268,12 +310,15 @@ public void close() throws IOException {
     int numFilesDeleted = 0;
 
     for (Entry entry : blocks.values()) {
+      entry.takeLock(Entry.LockType.WRITE);

Review Comment:
   should we be acquiring locks in close()?
   good: no race condition in close
   bad) the usual
   
   also, L303: should closed be atomic?





> s3a prefetch cache blocks should be accessed by RW locks
> --------------------------------------------------------
>
>                 Key: HADOOP-18740
>                 URL: https://issues.apache.org/jira/browse/HADOOP-18740
>             Project: Hadoop Common
>          Issue Type: Sub-task
>            Reporter: Viraj Jasani
>            Assignee: Viraj Jasani
>            Priority: Major
>              Labels: pull-request-available
>
> In order to implement LRU or LFU based cache removal policies for s3a 
> prefetched cache blocks, it is important for all cache reader threads to 
> acquire read lock and similarly cache file removal mechanism (fs close or 
> cache eviction) to acquire write lock before accessing the files.
> As we maintain the block entries in an in-memory map, we should be able to 
> introduce read-write lock per cache file entry, we don't need coarse-grained 
> lock shared by all entries.
>  
> This is a prerequisite to HADOOP-18291.



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