If exceptions occur in tasks running on 2 (or more) threads and we try to output backtraces concurrently, the output can have interleaved lines, making it difficult to figure out the actual stack for either exception.

Probably the best (only?) solution is to replace the use of jl_safe_printf() wherever it is used, and instead accumulate the entire backtrace into a buffer, then use a single jl_safe_printf to output the buffer.

Any other solutions?