I'm looking at the boost::stacktrace::safe_dump_to API and I cannot for the life of me work out how to determine how much space to allocate for the safe_dump_to() call. If I pass (nullptr, 0), it just returns 0, so that's not it. I could guess some constant number, but how do i know that's enough?
How to determinte how much space to allocate for boost::stacktrace::safe_dump_to?
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1 Answers
The docs specify:
This header contains low-level async-signal-safe functions for dumping call stacks. Dumps are binary serialized arrays of void*, so you could read them by using 'od -tx8 -An stacktrace_dump_failename' Linux command or using boost::stacktrace::stacktrace::from_dump functions.
Returns:
Stored call sequence depth including terminating zero frame. To get the actually consumed bytes multiply this value by the sizeof(boost::stacktrace::frame::native_frame_ptr_t))
It's not overly explicit, but this means you need sizeof(boost::stacktrace::frame::native_frame_ptr_t)*N where N is the number of stackframes in the trace.
Now of course, you can find out N, but there is not async-safe way to do allocate dynamically anyways, so you'd simply have to pick a number that suits your application. E.g. 256 frames might be reasonable, but you should look at your own needs (e.g. DEBUG builds will show a lot more stack frames, especially with code that heavily relies on template generics, YMMV).
Since the whole safe_dump_to construct is designed to be async-safe, I always just use the overload that writes to a file. When reading it back (typically after a restart) you will be able to deduce the number of frames from the file-size.
Optionally see some of my answers for code samples/more background information
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