A representation of a mutual-exclusion lock.
This class lets scripts make sure that only one instance of the script executes a given section of code at a time. This is particularly useful for callbacks and triggers, where a user action might cause changes to a shared resource and you want to ensure that there aren't collisions.
The following example shows how to use a lock in a form submit handler.
// Generates a unique ticket number for every form submission. function onFormSubmit(e) { const targetCell = e.range.offset(0, e.range.getNumColumns(), 1, 1); // Gets a script lock before modifying a shared resource. const lock = LockService.getScriptLock(); // Waits for up to 30 seconds for other processes to finish. lock.waitLock(30000); const scriptProperties = PropertiesService.getScriptProperties(); const ticketNumber = Number(scriptProperties.getProperty('lastTicketNumber')) + 1; scriptProperties.setProperty('lastTicketNumber', ticketNumber); // Releases the lock so that other processes can continue. lock.releaseLock(); targetCell.setValue(ticketNumber); }Without the Lock service, if two users submit the form at approximately the same time, the ticket numbers could end up the same, since the
lastTicketNumber
property could change after it
was read from the ScriptProperties
but before the new value was written back.Methods
Method | Return type | Brief description |
---|---|---|
has | Boolean | Returns true if the lock was acquired. |
release | void | Releases the lock, allowing other processes waiting on the lock to continue. |
try | Boolean | Attempts to acquire the lock, timing out after the provided number of milliseconds. |
wait | void | Attempts to acquire the lock, timing out with an exception after the provided number of milliseconds. |
Detailed documentation
hasLock()
Returns true if the lock was acquired. This method will return false if try
or
wait
were never called, timed out before the lock could be retrieved, or if release
was called.
const lock = LockService.getScriptLock(); lock.tryLock(10000); if (!lock.hasLock()) { Logger.log('Could not obtain lock after 10 seconds.'); }
Return
Boolean
— true if the lock was acquired, false otherwise
releaseLock()
Releases the lock, allowing other processes waiting on the lock to continue. The lock is automatically released when the script terminates, but for efficiency it is best to release it as soon as you no longer need exclusive access to a section of code. This method has no effect if the lock has not been acquired.
Note that if you are working with a spreadsheet, you should call SpreadsheetApp.flush() prior to releasing the lock, to commit all pending changes to the spreadsheet while you still have exclusive access to it.
const lock = LockService.getScriptLock(); lock.waitLock(10000); // Do some work on a shared resource. lock.releaseLock();
tryLock(timeoutInMillis)
Attempts to acquire the lock, timing out after the provided number of milliseconds. This method has no effect if the lock has already been acquired.
const lock = LockService.getScriptLock(); const success = lock.tryLock(10000); if (!success) { Logger.log('Could not obtain lock after 10 seconds.'); }
Parameters
Name | Type | Description |
---|---|---|
timeout | Integer | how long to wait to acquire the lock, in milliseconds |
Return
Boolean
— true if the lock was acquired, false otherwise
waitLock(timeoutInMillis)
Attempts to acquire the lock, timing out with an exception after the provided number of
milliseconds. This method is the same as try
except that it throws an exception
when the lock could not be acquired instead of returning false.
const lock = LockService.getScriptLock(); try { lock.waitLock(10000); } catch (e) { Logger.log('Could not obtain lock after 10 seconds.'); }
Parameters
Name | Type | Description |
---|---|---|
timeout | Integer | how long to wait to acquire the lock, in milliseconds |
Throws
Error
— if the method timed out before the lock was acquired