CODEWITHSUNDEEP
cunixgccsignals
shadyabhi
shadyabhi

Reputation: 17234

Calling a standard library function in signal handler

Why is calling a standard library function inside a signal handler discouraged?

Upvotes: 5

Views: 2949

Answers (4)

Roman Dmitrienko
Roman Dmitrienko

Reputation: 4235

It is all running fine and stuff, until you run into some mysterious bugs which are totally untraceable :)

man 7 signal will give you a list of system calls which are safe to call from a signal handler. It is described in POSIX as well.

Upvotes: 1

user50049
user50049

Reputation:

Its not only re-entrancy issues, depending on the signal being services you also want to avoid inadvertent calls to malloc() (i.e. asprintf()) and other variadic expansion (i.e. printf()).

Upvotes: 1

Paul R
Paul R

Reputation: 213080

Because the library function may not be reentrant.

Upvotes: 0

Macmade
Macmade

Reputation: 54029

This is explained in the GNU LibC documentation.

If you call a function in the handler, make sure it is reentrant with respect to signals, or else make sure that the signal cannot interrupt a call to a related function.

And just in case, here's the Wikipedia page on reentrant functions.

A computer program or routine is described as reentrant if it can be safely called again before its previous invocation has been completed (i.e it can be safely executed concurrently).

Upvotes: 11

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