PuTTY bug win-pageant-max-connections-2

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summary: Support more than 64 simultaneous connections to Windows Pageant named pipe
class: bug: This is clearly an actual problem we want fixed.
absent-in: 0.74
fixed-in: 17c57e1078c8fabd5417175247b38ce7b1643ca4 (0.77)

The new named-pipe transport for Windows Pageant, introduced in 0.75, was not able to handle more than 64 connections to the agent at the same time. This arose because of the limit on the number of handles you can pass to MsgWaitForMultipleObjects in the Windows API.

In 0.75, this had the particularly bad effect that you couldn't even have more than about 30 instances of PuTTY running at the same time which had ever authenticated with Pageant, because each instance of PuTTY accidentally kept two Pageant connection handles open for its whole lifetime.

That bug was fixed in 0.76, so each PuTTY closes its connection to Pageant when it no longer needs it. But the underlying bug remained: if you really did have more than 64 connections to Pageant open at once – for example, because you were running a very large number of parallel jobs on a server all using agent forwarding – then Pageant would lose track of some of the connections it was supposed to be waiting for, and eventually hang.

For 0.77, this should be properly fixed: Pageant can handle an arbitrary number of simultaneous connections without running into that Windows limit.

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