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How can a contract run itself at a later time?

up vote 14 down vote favorite

In my blockchain application, I would like to have an event triggered at a later time, hours or perhaps even days after the application has most recently received a transaction from a user. How can I create an "event" that will trigger after a certain amount of time has passed?

2 Answers

up vote 4 down vote accept

You could use the Ethereum Alarm Clock as previously mentioned, but you could also change your programming style to a "must call to execute" paradigm.

For instance, if you want to lock up money for a month until it gets returned, instead of actually having the money be sent after a month, you could have the user call a function that then returns the money.

up vote 3 down vote

There is no formal way to schedule events via the protocol itself.

However somebody already wrote an Ethereum Alarm Clock-contract that supports scheduling events at a later moment in time. It's decentralized as well as far as I could tell, anybody can fire scheduled events and get paid for doing so.


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How can a contract run itself at a later time?

up vote 14 down vote

In my blockchain application, I would like to have an event triggered at a later time, hours or perhaps even days after the application has most recently received a transaction from a user. How can I create an "event" that will trigger after a certain amount of time has passed?


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up vote 9 down vote

You could use the Ethereum Alarm Clock as previously mentioned, but you could also change your programming style to a "must call to execute" paradigm.

For instance, if you want to lock up money for a month until it gets returned, instead of actually having the money be sent after a month, you could have the user call a function that then returns the money.

edit

My ideal answer combines these top two by explaining when you should use one style vs the other. The answer, by the way, is that you should use a "must call to execute" paradigm for operations that affect only your own contract's state, and you should use the Ethereum Alarm clock for operations that need to update some state elsewhere in the blockchain (the state of someone who won't be calling your contract directly). - Jeff Coleman Jan 21 '16 at 0:11

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