Tuesday, November 20, 2018

Constraints on QuickLook Plug-ins

Alexandre Colucci:

A QuickLook plugin on macOS 10.14 has several constraints to satisfy. If one of the limits is exceeded, the plugin will immediately be killed and no preview will be visible. Having such restrictions makes sense but they appear to be undocumented. This article addresses the lack of information about these constraints.


On macOS 10.14, the QuickLook daemon applies 3 kinds of restrictions on the plugins:

  • maximum execution duration
  • maximum memory usage
  • maximum number of open file descriptors.

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I've noticed that QuickLook has degraded substantially in recent versions of macOS on multiple machines. It's often faster to open a file (even basic filetypes like JPG, PNG, or PDF) than it is to use QuickLook. I've tried just about all of the troubleshooting methods I can find online, like clearing the QL cache and running various command line tweaks, but without luck. In contrast, QuickLook on older Snow Leopard machines preview many of the same files immediately. It feels like QuickLook is another useful tool that is becoming unreliable in the Age of Emojis.

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