thread-safe vs async-signal safe

Question

In APUP section 12.5 ,mentioned that:

" If a function is reentrant with respect to multiple threads, we say that it is thread-safe. This doesn't tell us, however, whether the function is reentrant with respect to signal handlers."

I was confusing why a function is thread-safe but maybe not async-signal safe.

is there an example ?

Thanks

Answer 1

A function can be made thread-safe by protecting the state it modifies with a mutex. This is, however, not async-signal-safe since if you call the function e.g. from a signal handler the program can deadlock.

A common function with this property is malloc().