Meaning & use
semaphore
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Meanings
noununcountable
A way of sending messages over a distance by holding flags or arms in set positions, each representing a letter.
Grammar: Usually no article: they signaled in semaphore.
Patterns
- signal in semaphore
- send a message by semaphore
The sailors sent the warning by semaphore across the harbor.
Scouts often learn semaphore as a game.
He waved two flags in semaphore to spell his name.
nouncountable
A signaling device with movable arms, especially one used on railways to show a train whether it may proceed.
Grammar: Takes an article: the semaphore dropped to show a stop.
Patterns
- a railway semaphore
The old railway semaphore dropped to warn the driver.
A tall semaphore stood beside the track.
Museums sometimes restore a working semaphore.
nouncountablecomputingtechnical
A programming tool that controls how several processes or threads can use a shared resource at the same time.
Grammar: A computing use: the program uses a semaphore to avoid conflicts.
Patterns
- acquire a semaphore
- release a semaphore
The program uses a semaphore to limit how many threads read the file.
A thread must release the semaphore when it finishes.
Bugs appeared because the semaphore was never released.
Word forms
| plural | semaphores |
|---|
Common combinations
- signal in semaphore
- The two ships signaled in semaphore at dawn.
- semaphore flags
- She waved the red and yellow semaphore flags.
- railway semaphore
- The railway semaphore changed as the train approached.
- acquire a semaphore
- A process must acquire a semaphore before writing.
- semaphore signal
- The semaphore signal told us the line was clear.
Synonyms and how they differ
- flag signals
- Flag signals is a general phrase for any flag code, while semaphore is the specific system of arm positions.
- signal
- Signal is the broad word for any warning or message, and semaphore is one particular method.
- Morse code
- Morse code uses short and long signals of light or sound, while semaphore uses flags seen from a distance.
- mutex
- A mutex is a lock allowing one thread at a time, while a semaphore can allow a set number.
Word family
Commonly confused: semaphore or telegraph?
semaphore vs telegraph
A telegraph sends coded messages through wires, while semaphore uses visible flags or arms.
Practice
Two scouts stood on opposite hills and sent messages by holding flags in different positions. This is called ____.
Choose one answer.
Semaphore uses flag positions for letters. Morse code uses long and short signals, and a telegraph uses wires.
Make it your own
Write a sentence using “semaphore”, then check it and compare it with the examples above.