Hi, tl;dr when calling a function which takes multiple geometries, like GEOSUnion_r <https://libgeos.org/doxygen/geos__c_8h.html#afd3d82a6d039ab5637e0a8a066694b7d>, where the two geometries are associated with different contexts, do I have to ensure that both geometries' contexts are used exclusively?
Background: I maintain the Go bindings for GEOS <https://github.com/twpayne/go-geos>, which exclusively use the thread-safe *_r functions. Every created geometry is associated with a context. Every context has a mutex to ensure that it is only accessed from a single thread at time. For functions that take multiple geometries I check if the geometries are from different contexts, and if so, lock both mutexes. Here <https://github.com/twpayne/go-geos/blob/c9ed31526fa2ee3599ffe0fdf4556a6cf9c0b204/geommethods.go#L865-L875> is an example: // Union returns the union of g and other. func (g *Geom) Union(other *Geom) *Geom { g.mustNotBeDestroyed() g.context.Lock() defer g.context.Unlock() if other.context != g.context { other.context.Lock() defer other.context.Unlock() } return g.context.newGeom(C.GEOSUnion_r(g.context.handle, g.geom, other.geom), nil) } However, there is a potential deadlock if there are two geometries A and B owned by different contexts and A.Union(B) and B.Union(A) are called simultaneously from different threads. In practice this pattern is unlikely to occur, but I would like to guard against it. I checked the documentation on GEOS's C API <https://libgeos.org/usage/c_api/>, the GEOS developer notes <https://github.com/libgeos/geos/blob/main/DEVELOPER-NOTES.md>, did a superficial search of the GitHub issues <https://github.com/search?q=repo%3Alibgeos%2Fgeos+context&type=issues>, and a superficial search of the geos-devel <https://www.google.com/search?q=site%3Alists.osgeo.org+%22%5Bgeos-devel%5D%22+context> archives, and could not find an answer to this question. Many thanks for any insight, Tom
