17 Language support library [support]

17.13 Other runtime support [support.runtime]

17.13.5 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 [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 of class atomic_flag, or
  • f is a non-member function, and the first parameter of f has type cv atomic_flag*, 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;
    [Note 1: 
    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])196 ; 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/IEC 9899:2018, 7.14
196)196)
Such initialization can occur because it is the first odr-use ([basic.def.odr]) of that variable.