Class Lock

Lock

A representation of a mutual-exclusion lock.

This class allows scripts to make sure that only one instance of the script is executing a given section of code at a time. This is particularly useful for callbacks and triggers, where a user action may cause changes to a shared resource and you want to ensure that aren't collisions.

The following examples shows how to use a lock in a form submit handler.

// Generates a unique ticket number for every form submission.
function onFormSubmit(e) {
  var targetCell = e.range.offset(0, e.range.getNumColumns(), 1, 1);

  // Get a script lock, because we're about to modify a shared resource.
  var lock = LockService.getScriptLock();
  // Wait for up to 30 seconds for other processes to finish.
  lock.waitLock(30000);

  var ticketNumber = Number(ScriptProperties.getProperty('lastTicketNumber')) + 1;
  ScriptProperties.setProperty('lastTicketNumber', ticketNumber);

  // Release the lock so that other processes can continue.
  lock.releaseLock();

  targetCell.setValue(ticketNumber);
}

Without the LockService, 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
hasLock()	Boolean	Returns true if the lock was acquired.
releaseLock()	void	Releases the lock, allowing other processes waiting on the lock to continue.
tryLock(timeoutInMillis)	Boolean	Attempts to acquire the lock, timing out after the provided number of milliseconds.
waitLock(timeoutInMillis)	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 tryLock(timeoutInMillis) or waitLock(timeoutInMillis) were never called, timed out before the lock could be retrieved, or if releaseLock() was called.

var 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.

var 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.

var lock = LockService.getScriptLock();
var success = lock.tryLock(10000);
if (!success) {
  Logger.log('Could not obtain lock after 10 seconds.');
}

Parameters

Name	Type	Description
timeoutInMillis	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 tryLock(timeoutInMillis) except that it throws an exception when the lock could not be acquired instead of returning false.

var lock = LockService.getScriptLock();
try {
  lock.waitLock(10000);
} catch (e) {
  Logger.log('Could not obtain lock after 10 seconds.');
}

Parameters

Name	Type	Description
timeoutInMillis	Integer	how long to wait to acquire the lock, in milliseconds

Throws

Error — if the method timed out before the lock was acquired