Where does lock collide?

In concurrent programming, a lock is a synchronization primitive that enforces mutually exclusive access to a shared resource, so that only one thread at a time may enter a protected region while the others wait their turn. Dijkstra's 1965 Solution of a problem in concurrent programming control posed and solved the mutual exclusion problem that a lock answers, and the same idea underlies the mutex; when two threads each hold one lock and wait for the other, the program can deadlock and freeze. Here the lock is an abstract control mechanism in software, a rule about who may proceed, and it has nothing to do with the fit between an enzyme and its substrate, a chamber that lifts boats, or a bolt on a door.[1]

Unit

One synchronization primitive guarding a shared resource, held by at most one thread at a time

Recovery means

A held lock is released when the thread leaves the protected region, letting a waiting thread proceed

Measured by

Observed through contention, wait times, and hold durations, and by detecting deadlock or lock ordering in the code

In biochemistry, the lock and key model is Emil Fischer's hypothesis that an enzyme's active site fits its substrate with the precise complementarity of a lock and its key, which explains why an enzyme acts on one molecule and ignores others. Fischer's 1894 Einfluss der Configuration auf die Wirkung der Enzyme proposed this fit to account for enzyme specificity, and it was later refined by the induced-fit model, in which the site reshapes as the substrate binds. Here the lock is a metaphor for molecular shape matching, a way of picturing specificity, and it is not a software rule about thread access, a canal chamber, or a mechanical bolt.[2]

Unit

A metaphor for the shape complementarity between one enzyme's active site and its substrate

Recovery means

Not applicable

Measured by

Inferred from binding specificity and reaction rates, and later from crystal structures of enzyme and substrate together