Час через дієприкметник: -ते ही, -ते-ते

Three shapes

• घर पहुँचते ही उसने फ़ोन किया। - The moment he got home he phoned.
• बात करते-करते वह सो गया। - He fell asleep while talking.
• ट्रेन छूटते-छूटते बची। - The train very nearly left.

-ते-ते has a second sense

With a perfective it means 'almost': गिरते-गिरते बचा - he nearly fell. This is idiomatic and worth learning as a unit.

The subject stays shared

Like the -कर participle, these require the same subject in both halves.