Class Lock

Lock

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) {
  var targetCell = e.range.offset(0, e.range.getNumColumns(), 1, 1);

  // Gets a script lock before modifying a shared resource.
  var lock = LockService.getScriptLock();
  // Waits for up to 30 seconds for other processes to finish.
  lock.waitLock(30000);

  var 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

MethodReturn typeBrief description
hasLock()BooleanReturns true if the lock was acquired.
releaseLock()voidReleases the lock, allowing other processes waiting on the lock to continue.
tryLock(timeoutInMillis)BooleanAttempts to acquire the lock, timing out after the provided number of milliseconds.
waitLock(timeoutInMillis)voidAttempts 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

NameTypeDescription
timeoutInMillisIntegerhow 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

NameTypeDescription
timeoutInMillisIntegerhow long to wait to acquire the lock, in milliseconds

Throws

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