I've been using Boinc since 2014. Recently, when leaving my laptop unattended, I've been coming back to a black screen (sometimes a working mouse pointer) and the fans running on full blast. I can't get the OSX login to come up and it all seems locked up. So I have to restart it to get the system responsive again. This problem started happening during the month of March.

Yosemite, 10.10.2, latest patches, Boinc 7.4.36. Cuda 6.5.37. Boinc's using GPU.

I'm unclear what has changed this month to start this problem (Boinc or Osx).

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I have a suspicion that the relationship is between using the GPU (even when the computer is busy, or not, I don't know) and the Screen Saver. I'm running some tests to see if I can reproduce the problem in a deterministic way.

I say this because that IS something I changed. I wanted to leverage the higher performance from the GPU and started fiddling with the GPU related preferences.
I also was on CUDA driver 6.5.37. There's an update out. I'll update that as well.

This project doesn't use the gpu, so if IT'S the problem, then it's some other program that uses it intensely that's causing the problem.
But Yosemite is known to cause problems when it runs BOINC stuff.

Freezing black screen (other than mouse pointer) doesn't happen if the boinc screen saver is turned off.
I've updated to latest Boinc and cuda drivers. It still happens although rarely (maybe once a week) where before it happened *every time* the screen saver turned on.