Block allocation method does not check pendingCreates for duplicate block ids

The HDFS namenode allocates a new random blockid when requested. It then checks the blocksMap to verify if this blockid is already in use. If this block is is already in use, it generates another random number and above process continues. When a blocksid that does not exist in the blocksMap is found, it stores this blocksid in pendingCreateBlocks and returns the blocksid to the requesting client.

The above check for detecting duplicate blockid should check pendingCreateBlocks as well.

A related problem exists when a file is deleted. Deleting a file causes all its blocks to be deleted from the blocksMap immediately. These blockids move to recentInvalidateSets and are sent out to the corresponding datanodes as part of responses to succeeding heartbeats. So, there is a time window when a block exists in the datanode but not in the blocksMap. At this time, if the blockid-random-number generator generates a blockid that exists in the datanode but not on the blocksMap, then the namenode will fail to detect that this is a duplicate blockid.