PuTTY bug win-pageant-concurrent-startup

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summary: Starting Windows Pageant multiple times concurrently could fail
class: bug: This is clearly an actual problem we want fixed.
difficulty: fun: Just needs tuits, and not many of them.
fixed-in: 0ad344ca32e3df0d33883eed662f6aef6eff3a11 (0.77)

When Windows Pageant starts up, it checks whether an instance of itself is already running. If so, then it acts as a client to the existing instance, and then shuts down. (This way, you can run a command like 'pageant mykey.ppk' from a shortcut, and the key will be added to your existing Pageant if one is running, rather than starting a second Pageant server which will fight with it.)

But that check was not adequately protected against two Pageants starting up at exactly the same time. This could happen, for example, if you put shortcuts to two or more private key files in your Windows startup folder (with Pageant configured as the handler for that file extension), so that Windows would launch them simultaneously.

For 0.77, this has been fixed to use the same mutex mechanism that PuTTY's connection sharing uses to atomically decide which PuTTY is upstream and which are the downstreams. So now, the simultaneously started Pageants should reliably agree on one of themselves to be the server, and the rest should add their keys to it.

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Audit trail for this bug.
(last revision of this bug record was at 2022-05-15 14:15:31 +0100)