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https://issues.apache.org/jira/browse/ARROW-1775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16242966#comment-16242966
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ASF GitHub Bot commented on ARROW-1775:
---------------------------------------
wesm commented on a change in pull request #1289: ARROW-1775: Ability to abort
created but unsealed Plasma objects
URL: https://github.com/apache/arrow/pull/1289#discussion_r149512465
##########
File path: cpp/src/plasma/client.cc
##########
@@ -278,6 +278,43 @@ Status PlasmaClient::Get(const ObjectID* object_ids,
int64_t num_objects,
return Status::OK();
}
+/// This is a helper method for unmapping objects for which all references have
+/// gone out of scope, either by calling Release or Abort.
+///
+/// @param object_id The object ID whose data we should unmap.
+Status PlasmaClient::UnmapObject(const ObjectID& object_id) {
+ auto object_entry = objects_in_use_.find(object_id);
+ ARROW_CHECK(object_entry != objects_in_use_.end());
+ ARROW_CHECK(object_entry->second->count == 0);
+
+ // Decrement the count of the number of objects in this memory-mapped file
+ // that the client is using. The corresponding increment should have
+ // happened in plasma_get.
+ int fd = object_entry->second->object.handle.store_fd;
+ auto entry = mmap_table_.find(fd);
+ ARROW_CHECK(entry != mmap_table_.end());
+ ARROW_CHECK(entry->second.count >= 1);
+ if (entry->second.count == 1) {
+ // If no other objects are being used, then unmap the file.
+ int err = munmap(entry->second.pointer, entry->second.length);
+ if (err == -1) {
+ return Status::IOError("Error during munmap");
+ }
+ // Remove the corresponding entry from the hash table.
+ mmap_table_.erase(fd);
Review comment:
If munmap fails, what should happen to this `fd`? I guess it would be an
esoteric failure
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> Ability to abort created but unsealed Plasma objects
> ----------------------------------------------------
>
> Key: ARROW-1775
> URL: https://issues.apache.org/jira/browse/ARROW-1775
> Project: Apache Arrow
> Issue Type: New Feature
> Components: Plasma (C++)
> Reporter: Stephanie Wang
> Labels: pull-request-available
>
> It would be useful to allow a Plasma client to abort an object that it
> created but hasn't yet sealed. After the abort, it should appear as if the
> object was never created all. The logic is similar to the delete case, except
> that the client must release the object atomically with the removal of the
> object from the cache and store.
> In Ray, for example, we need this for the distributed version of the Plasma
> store, where many Plasma clients transfer objects to each other. If a sending
> Plasma client fails during a transfer, we want to make sure that the
> receiving client can abort the transfer, so that we can later recreate the
> object successfully. Otherwise, we will fail with an error that the object
> already exists.
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