Optimize getting caller location using some ruby internals #20
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ext/rotoscope/callsite.c
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| size_t ruby_control_frame_size; | ||
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| // MRI ruby control frames are stored in an array as of | ||
| // ruby 2.4.1, so we depend on this to be able to get the |
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grammar nit "we depend on this to be able to get the determine the control…"
ext/rotoscope/rotoscope.h
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| @@ -3,6 +3,8 @@ | |||
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| #include "unistd.h" | |||
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| #include "callsite.h" | |||
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If we don't need any of the types for rotoscope.h does it make sense to move this include into rotoscope.c? That's what I've done with the other includes but I don't know what's more standard (I'm aware they're functionally equivalent though)
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Ya, I could move it into rotoscope.c
ext/rotoscope/callsite.c
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| size_t ruby_control_frame_size; | ||
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| // MRI ruby control frames are stored in an array as of | ||
| // ruby 2.4.1, so we depend on this to be able to get the |
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I was under the impression we were able to successfully advance the frame pointer in 2.3.3 as well. Do we need a #ifdef guard in this code for the ruby version?
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Oops, I didn't really say that properly. I meant to say that this is the behaviour at least until ruby 2.4.1, since I can't predict the future.
We want to get the caller's control frame path and line number in a trace event hook without the overhead of going through a method like `caller` or `caller_locations`. The ruby tracepoint API only gives access to the called functions path and line number. Instead, we rely on the minimum amount or ruby internals needed to get the caller's path and line number by changing the `cfp` field of the internal rb_trace_arg_struct before getting the path and lineno from the trace arg.
dylanahsmith
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Fixes #16
Problem
We want to get the caller's control frame path and line number in a trace event hook without the overhead of going through a method like
callerorcaller_locations. The ruby tracepoint API only gives access to the current frames path and line number.Solution
Get the caller frame's path and line number by modifying the internal
cfpfield of the trace arg to point to the caller's control frame. This means changes to this rb_trace_arg_struct struct in ruby could break the library.The caller's control frame can be found by adding the size of a control frame to the
cfp. Therb_control_frame_tis also internal to ruby, so we determine this by getting the difference between thecfpfor two nested function calls during initialization.Since we are depending on ruby internals, even a patch release of ruby could break this gem. However, I did minimize the amount of internals that this patch depends on to reduce the chance of it breaking in the future.