Posts (238+)

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July 2026

Concurrent Queues and Skip Lists:Lock-Free Ends and Concurrent Order

Use ConcurrentLinkedQueue and ConcurrentLinkedDeque for non-blocking ends, and ConcurrentSkipListMap/Set when you need a concurrent sorted map — not a BlockingQueue and not a HashMap.

Algorithms

External Sort:K-Way Merge When the File Does Not Fit in RAM

Sort RAM-sized chunks, write runs to disk, then k-way merge with a heap of heads — the in-memory merge-sort cousin when the file cannot be loaded.

Java

BlockingQueue:Hand Off Work Without a Busy Wait

Use BlockingQueue to pass work between threads — put/take that block, offer/poll with timeouts, and when to pick Array, Linked, Delay, Synchronous, or Transfer queues.

Algorithms

Timsort:What `Arrays.sort` Actually Runs on Objects

Natural runs, insertion on short runs, then merge — what object Arrays.sort and Collections.sort actually run, and why you should not hand-roll it.

Java

Copy-On-Write:Snapshot Iterators When Reads Dominate

Use CopyOnWriteArrayList and CopyOnWriteArraySet when iteration is the hot path — every mutation copies the array, and iterators walk a snapshot.

Algorithms

Radix Sort:Digit Passes When Comparison Is the Wrong Primitive

LSD digit passes as counting sort, when integer or string keys have a digit layout, and why Arrays.sort is not this.

Java

ConcurrentHashMap:Shared Maps Without Synchronizing the Whole Table

Use ConcurrentHashMap for a shared map — per-bin concurrency, no nulls, weakly consistent iterators, and atomic compute/merge — not Hashtable and not synchronizedMap.

Algorithms

Counting Sort:Rank by Frequency When the Key Universe Is Small

Histogram, prefix of counts, and a stable place-from-the-right pass when keys come from a small universe.

Linux

Linux rsync:Sync Files Efficiently, Locally and Remote

Hands-on rsync recipes for everyday work — incremental sync, remote backups over SSH, progress output, and safe dry-runs.

Java

Legacy Collections:Vector, Stack, Hashtable, and Why They Still Compile

Recognize Vector, Stack, Hashtable, Dictionary, Enumeration, and Properties as legacy — synchronized whole-table types you should not choose for new code.