Vector clocks reveal two concurrent writes
Compare three-component version vectors, reconcile a shopping-list deletion, and test how identity reuse or erased context breaks causal comparison.
Foundation
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A little theory. A lot of practice.
A lost update in six small steps
Trace two increments that lose an update, define the critical section, and distinguish a teaching interleaving from undefined C++ data races.
Foundation
File descriptors: two handles can share one offset
Compare inherited descriptors with independent open calls using a six-byte file, and explain shared offsets, close behavior and close-on-exec.
Foundation
The CSS box model when a card will not fit
Calculate content, padding, borders and margins to diagnose an overflowing card, then distinguish box sizing from minimum sizes and transformed rectangles.
Foundation
Cache-aside and the stale fill race
Interleave a source read, commit, invalidation and late fill, then test how an atomic generation guard rejects obsolete cache writes.
Foundation
Focus styles that survive a theme switch
Preserve the focused control across theme changes, retain a pointer fallback, and verify clipping, viewport clearance and forced-color behavior.
Foundation
An LRU trace you can run by hand
Trace hits, recency changes and evictions in a three-entry Python cache, then check loader failures, cached None and a scan that misses every time.
Foundation
TTL cache freshness depends on when you start the clock
Compare selection-time and arrival-time TTLs, test exact expiration boundaries, and carry response age through an explicit HTTP caching example.
Foundation
Read the cascade before adding important
Trace a link color through layers, inline styles, specificity and scope with six reversible experiments before adding CSS overrides.
Foundation
Flexbox for a toolbar with one flexible child
Relax the document wrapper’s automatic flex minimum, inspect action containment, and add wrapping plus a keyboard-accessible full filename.
Foundation
Mutex ownership and a bounded work queue
Protect a bounded ring queue as one state transition, including its head, tail and count, and state what the mutex does not guarantee.
Foundation
A timeout leaves the remote outcome uncertain
Run local TCP controls where the same client timeout hides different server outcomes, then test retry identities and lost deduplication receipts.
Foundation