Dynamic tracing for R.
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Nested hook execution is disallowed by the framework. Hooks intercept execution of R interpreter code. If one hook triggers another, then the triggered hook is intercepting code that is executed by the hook and not by the program being traced. This is likely not what you intended to do. When such a situation arises, the framework prints the name of the currently active hook and of the hook being triggered by it; and exits.
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Garbage collection is turned off by the framework before entry into the hook and reinstated upon exit. This reduces the probability of the hook code triggering garbage collection. The hook code can still rely on the interpreter's C code which can turn on garbage collection. Hence, the mechanism is not foolproof and care has to taken when calling the interpreter code. Even if such a situation happens, the framework will detect it and stop the execution of the program. This is because when the garbage collector is triggered, a hook inside the garbage collector gets triggered. This nested hook execution is detected by the framework.
# to build the R interpreter and the tracer
./build.sh
# to build the tracer
./build-tracer.shRdt(tracer="promises", block={1+1}, format="sql")
trace.promises.r({1+1})
trace.promises.sql({1+1}) # save to file = trace.sql
trace.promises.sql({1+1}, output=CONSOLE) #other outputs are FILE, DB
trace.promises.db({1+1}) # tracer.sqlite uses PSQL
trace.promises.uncompiled.db({1+1}) # tracer.sqlite uses SQL