maya-headless-batch

Heavy Maya work, out of process

Applies to any long or risky Maya operation, not one project's render. The measurements here were taken in-vivo on Maya 2027 / macOS Tahoe; none of it is inferable from the API docs.

For which command or flag to call, use search_maya_docs — that is the reference layer. This skill is the decision of where to run, and what fails silently when you run it in the wrong place.

1. The Command Port is Maya's main thread

maya_session(action="execute_python") executes synchronously on Maya's main thread. Default wait is 10 s, timeout raises it to 600 s, heartbeats stream every 10 s. For the whole of that window the GUI is frozen.

So a long op is not "slow" — it is a hang that looks like a crash, and on Maya 2027 / Tahoe it frequently becomes one. Three GUI crash modes are known on that build (OpenGL paint, SynHub syscall, Qt hide), and chained heavy operations have taken the session down on their own.

Leave the Command Port when any of these is true:

• the work touches more than one scene file, or loops over frames;
• it opens or saves scenes in sequence;
• it renders anything;
• it exports or imports a cache;
• the artist's session must survive, or must not be disturbed.

Staying on the Command Port is right for: inspecting the open scene, small edits the artist wants to see, anything that must act on unsaved in-memory state. That last one is the real constraint — a headless run only sees what is on disk.

2. What maya.standalone does not give you

Plugins do not auto-load. This is the number-one headless failure. A bare standalone session loads none of them, so cmds.AbcExport, cmds.mayaUSDExport, cmds.FBXExport and cmds.arnoldExportAss simply do not exist until you load their plugin. The symptom is an AttributeError on a command you know is real.

Canonical pipeline set — load each in its own try, never abort the run on one:

mayaUsdPlugin   AbcImport   AbcExport   fbxmaya   objExport   mtoa