Differential D11143 Diff 27053 webroot/rsrc/externals/javelin/lib/Leader.js

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webroot/rsrc/externals/javelin/lib/Leader.js

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* used in conjunction with @{method:callIfLeader} to allow multiple event		* used in conjunction with @{method:callIfLeader} to allow multiple event
* responders to trigger a reaction to an event (like a sound) and ensure that		* responders to trigger a reaction to an event (like a sound) and ensure that
* it is played only once (not once for each notification), and by only one		* it is played only once (not once for each notification), and by only one
* tab (not once for each tab).		* tab (not once for each tab).
*		*
* Finally, tabs can register a callback which will run if they become the		* Finally, tabs can register a callback which will run if they become the
* leading tab, by listening for `onBecomeLeader`.		* leading tab, by listening for `onBecomeLeader`.
*/		*/

JX.install('Leader', {		JX.install('Leader', {

events: ['onBecomeLeader', 'onReceiveBroadcast'],		events: ['onBecomeLeader', 'onReceiveBroadcast'],

statics: {		statics: {
_interval: null,		_interval: null,
_broadcastKey: 'JX.Leader.broadcast',		_broadcastKey: 'JX.Leader.broadcast',
_leaderKey: 'JX.Leader.id',		_leaderKey: 'JX.Leader.id',
Show All 30 Lines	statics: {
/**		/**
* Call a method if this tab is the leader.		* Call a method if this tab is the leader.
*		*
* This is asynchronous because leadership election is asynchronous. If		* This is asynchronous because leadership election is asynchronous. If
* the current tab is not the leader after any election takes place, the		* the current tab is not the leader after any election takes place, the
* callback will not be invoked.		* callback will not be invoked.
*/		*/
callIfLeader: function(callback) {		callIfLeader: function(callback) {
		JX.Leader._callIf(callback, JX.bag);
		},


		/**
		* Call a method after leader election.
		*
		* This is asynchronous because leadership election is asynchronous. The
		* callback will be invoked after election takes place.
		*
		* This method is useful if you want to invoke a callback no matter what,
		* but the callback behavior depends on whether this is the leader or
		* not.
		*/
		call: function(callback) {
		JX.Leader._callIf(callback, callback);
		},
		epriestleyAuthorUnsubmitted Not Done Inline Actions I needed an "always call after election" method. epriestley: I needed an "always call after election" method.

		/**
		* Elect a leader, then invoke either a leader callback or a follower
		* callback.
		*/
		_callIf: function(leader_callback, follower_callback) {

if (!window.localStorage) {		if (!window.localStorage) {
// If we don't have localStorage, pretend we're the only tab.		// If we don't have localStorage, pretend we're the only tab.
self._becomeLeader();		self._becomeLeader();
callback();		leader_callback();
return;		return;
}		}

var self = JX.Leader;		var self = JX.Leader;

// If we don't have an ID for this tab yet, generate one and register		// If we don't have an ID for this tab yet, generate one and register
// event listeners.		// event listeners.
if (!self._id) {		if (!self._id) {
Show All 13 Lines	_callIf: function(leader_callback, follower_callback) {
// If we haven't installed an update timer yet, do so now. This will		// If we haven't installed an update timer yet, do so now. This will
// renew our lease every 5 seconds, making sure we hold it until the		// renew our lease every 5 seconds, making sure we hold it until the
// tab is closed.		// tab is closed.
if (!self._interval && lease.until > now + 10000) {		if (!self._interval && lease.until > now + 10000) {
self._interval = window.setInterval(self._write, 5000);		self._interval = window.setInterval(self._write, 5000);
}		}

self._becomeLeader();		self._becomeLeader();
callback();		leader_callback();
		} else {
		follower_callback();
}		}
return;		return;
}		}

// If the lease isn't good, try to become the leader. We don't have		// If the lease isn't good, try to become the leader. We don't have
// proper locking primitives for this, but can do a relatively good		// proper locking primitives for this, but can do a relatively good
// job. The algorithm here is:		// job. The algorithm here is:
//		//
Show All 9 Lines	_callIf: function(leader_callback, follower_callback) {
// This approximately follows an algorithm attributed to Fischer in		// This approximately follows an algorithm attributed to Fischer in
// "A Fast Mutual Exclusion Algorithm" (Leslie Lamport, 1985). That		// "A Fast Mutual Exclusion Algorithm" (Leslie Lamport, 1985). That
// paper also describes a faster (but more complex) algorithm, but		// paper also describes a faster (but more complex) algorithm, but
// it's not problematic to add a significant delay here because		// it's not problematic to add a significant delay here because
// leader election is not especially performance-sensitive.		// leader election is not especially performance-sensitive.

self._write();		self._write();

window.setTimeout(JX.bind(null, self.callIfLeader, callback), 50);		window.setTimeout(
		JX.bind(null, self._callIf, leader_callback, follower_callback),
		50);
},		},


/**		/**
* Send a message to all open tabs.		* Send a message to all open tabs.
*		*
* Tabs can receive messages by listening to `onReceiveBroadcast`.		* Tabs can receive messages by listening to `onReceiveBroadcast`.
*		*
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