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cppdraft/support/signal.md

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+[support.signal]
+
+# 17 Language support library [[support]](./#support)
+
+## 17.14 Other runtime support [[support.runtime]](support.runtime#support.signal)
+
+### 17.14.5 Signal handlers [support.signal]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6491)
+
+A call to the function signal synchronizes with any resulting
+invocation of the signal handler so installed[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6495)
+
+A [*plain lock-free atomic operation*](#def:plain_lock-free_atomic_operation "17.14.5 Signal handlers [support.signal]") is
+an invocation of a function f from [[atomics]](atomics "32.5 Atomic operations"),
+such that:
+
+- [(2.1)](#2.1)
+
+f is the function atomic_is_lock_free(), or
+
+- [(2.2)](#2.2)
+
+f is the member function is_lock_free(), or
+
+- [(2.3)](#2.3)
+
+f is a non-static member function of class atomic_flag, or
+
+- [(2.4)](#2.4)
+
+f is a non-member function, and
+the first parameter of f has type cv atomic_flag*, or
+
+- [(2.5)](#2.5)
+
+f is a non-static member function invoked on an object A,
+such that A.is_lock_free() yields true, or
+
+- [(2.6)](#2.6)
+
+f is a non-member function, and
+for every pointer-to-atomic argument A passed to f,atomic_is_lock_free(A) yields true[.](#2.sentence-1)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6523)
+
+An evaluation is [*signal-safe*](#def:evaluation,signal-safe "17.14.5 Signal handlers [support.signal]") unless it includes one of the following:
+
+- [(3.1)](#3.1)
+
+a call to any standard library function,
+except for plain lock-free atomic operations and
+functions explicitly identified as signal-safe;
+  [*Note [1](#note-1)*:
+  This implicitly excludes the use of new and delete expressions
+that rely on a library-provided memory allocator[.](#3.1.sentence-1)
+ — *end note*]
+
+- [(3.2)](#3.2)
+
+an access to an object with thread storage duration;
+
+- [(3.3)](#3.3)
+
+a dynamic_cast expression;
+
+- [(3.4)](#3.4)
+
+throwing of an exception;
+
+- [(3.5)](#3.5)
+
+control entering a [*try-block*](except.pre#nt:try-block "14.1 Preamble [except.pre]") or [*function-try-block*](except.pre#nt:function-try-block "14.1 Preamble [except.pre]");
+
+- [(3.6)](#3.6)
+
+initialization of a variable with static storage duration
+requiring dynamic initialization ([[basic.start.dynamic]](basic.start.dynamic "6.10.3.3 Dynamic initialization of non-block variables"), [[stmt.dcl]](stmt.dcl "8.10 Declaration statement"))[191](#footnote-191 "Such initialization can occur because it is the first odr-use ([term.odr.use]) of that variable.") ; or
+
+- [(3.7)](#3.7)
+
+waiting for the completion of the initialization of a variable with static storage duration ([[stmt.dcl]](stmt.dcl "8.10 Declaration statement"))[.](#3.sentence-1)
+
+A signal handler invocation has undefined behavior if it includes
+an evaluation that is not signal-safe[.](#3.sentence-2)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/support.tex#L6563)
+
+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[.](#4.sentence-1)
+
+See also: ISO/IEC 9899:2024, 7.14
+
+[191)](#footnote-191)[191)](#footnoteref-191)
+
+Such initialization can occur because it is the first odr-use ([[basic.def.odr]](basic.def.odr#term.odr.use "6.3 One-definition rule")) of that variable[.](#footnote-191.sentence-1)