Creating a lock system by utilizing GM_getValue and GM_setValue functions

Question

Creating a lock system by utilizing GM_getValue and GM_setValue functions

I have a script in Greasemonkey that checks for updates and prompts the user to download if necessary. The issue arises when multiple tabs are opened simultaneously, causing the script to notify the user in each tab at the same time, which can be frustrating.

The only way I can communicate between instances of the script is through GM_setValue/GM_getValue, giving access to a key/value store.

I am looking to implement a locking system (let's call it GM_setLock/GM_releaseLock) to manage this situation:

GM_setLock();
const tried_update = GM_getValue(available_version);
GM_setValue(available_version, true);
GM_releaseLock();

if (!tried_update) { prompt_user() }

Without locking, multiple instances could read the value before any of them actually set it, resulting in the user being notified more than once.

However, figuring out how to implement locking with just atomic read and write operations - without return previous value capability - is challenging. Any suggestions?

javascript locking greasemonkey

Answer 1

Answer №1

If you're working in Greasemonkey, the syntax might not allow for direct implementation of what you need. However, a similar approach can achieve your desired outcome:

Start by wrapping the upgrade check or relevant function like this:

function RunUpgradeCheck ()
{
    //--- Insert your code here.

    alert ("Upgrade check complete!");
}

.
Next, define RunOnceAcrossTabs() as shown below:

function RunOnceAcrossTabs (lockName, func)
{
    var storedValue = GM_getValue (lockName);
    if (storedValue)
    {
        //--- Add optional timestamp check to clear any old locks.
        return;
    }

    GM_setValue (lockName, new Date().toString());

    //--- Execute the specified function.
    (func)();

    //--- Clear the lock.
    GM_deleteValue (lockName);
}

.
Finally, call the function like this:

RunOnceAcrossTabs("UpgradeLock", RunUpgradeCheck);

Answer 2

If you're working in Greasemonkey, the syntax might not allow for direct implementation of what you need. However, a similar approach can achieve your desired outcome:

Start by wrapping the upgrade check or relevant function like this:

function RunUpgradeCheck ()
{
    //--- Insert your code here.

    alert ("Upgrade check complete!");
}

.
Next, define RunOnceAcrossTabs() as shown below:

function RunOnceAcrossTabs (lockName, func)
{
    var storedValue = GM_getValue (lockName);
    if (storedValue)
    {
        //--- Add optional timestamp check to clear any old locks.
        return;
    }

    GM_setValue (lockName, new Date().toString());

    //--- Execute the specified function.
    (func)();

    //--- Clear the lock.
    GM_deleteValue (lockName);
}

.
Finally, call the function like this:

RunOnceAcrossTabs("UpgradeLock", RunUpgradeCheck);

Creating a lock system by utilizing GM_getValue and GM_setValue functions

Answer №1

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