21 Language support library [language.support]

21.10 Other runtime support [support.runtime]

21.10.4 Signal handlers [support.signal]

A call to the function signal synchronizes with any resulting invocation of the signal handler so installed.
A plain lock-free atomic operation is an invocation of a function f from Clause [atomics], such that:
  • f is the function atomic_­is_­lock_­free(), or
  • f is the member function is_­lock_­free(), or
  • f is a non-static member function invoked on an object A, such that A.is_­lock_­free() yields true, or
  • f is a non-member function, and for every pointer-to-atomic argument A passed to f, atomic_­is_­lock_­free(A) yields true.
An evaluation is signal-safe unless it includes one of the following:
  • a call to any standard library function, except for plain lock-free atomic operations and functions explicitly identified as signal-safe.
    This implicitly excludes the use of new and delete expressions that rely on a library-provided memory allocator.
    end note
  • an access to an object with thread storage duration;
  • a dynamic_­cast expression;
  • throwing of an exception;
  • control entering a try-block or function-try-block;
  • initialization of a variable with static storage duration requiring dynamic initialization ([basic.start.dynamic], [stmt.dcl])220; or
  • waiting for the completion of the initialization of a variable with static storage duration ([stmt.dcl]).
A signal handler invocation has undefined behavior if it includes an evaluation that is not signal-safe.
The function signal is signal-safe if it is invoked with the first argument equal to the signal number corresponding to the signal that caused the invocation of the handler.
See also: ISO C 7.
Such initialization might occur because it is the first odr-use ([basic.def.odr]) of that variable.