The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that document the exact semantics of the language extension.
Add new text after paragraph 1
Within either execution environment, a thread is a flow of control within a program. It is implementation defined whether or not there may be more than one thread associated with a program. It is implementation defined how threads beyond the first are created, the name and type of the function called at thread startup, and how threads may be terminated. However, objects with thread storage duration shall be initialized before thread startup.
Add new text before paragraph 3
An object whose identifier is declared with the storage-class specifier
__threadhas thread storage duration. Its lifetime is the entire execution of the thread, and its stored value is initialized only once, prior to thread startup.
__thread to the list of storage class specifiers in
Change paragraph 2 to
With the exception of
__thread, at most one storage-class specifier may be given [...]. The
__threadspecifier may be used alone, or immediately following
Add new text after paragraph 6
The declaration of an identifier for a variable that has block scope that specifies
__threadshall also specify either
__threadspecifier shall be used only with variables.