Re: SIGALRM in a class member?
On Aug 13, 5:32 am, Jack Klein <jackkl...@spamcop.net> wrote:
On Tue, 12 Aug 2008 23:58:11 GMT, Ron Eggler <unkn...@example.com>
wrote in comp.lang.c++:
While you've made a number of important points:
[...]
Note the reference to the C signal handler definition, which states:
"If the signal occurs other than as the result of calling the
abort or raise function, the behavior is undefined if the
signal handler calls any function in the standard library
other than the signal function itself (with a first argument
of the signal number corresponding to the signal that caused
the invocation of the handler) or refers to any object with
static storage duration other than by assigning a value to a
static storage duration variable of type volatile
sig_atomic_t. Furthermore, if such a call to the signal
function results in a SIG-ERR return, the value of errno is
indeterminate."
Then, in a footnote, the C standard adds:
"If any signal is generated by an asynchronous signal handier,
the behavior is undefined."
In other words, according to the C standard, any signal
generated by SIGALRM is undefined behavior. That's true, but if
he's requesting a SIGALRM, he's working under an OS and with a
compiler which supports it, and defines some of the behavior the
C and C++ standards leave undefined. If he's on a Posix
system, what he can and cannot do is defined by the Posix
standard. And while it's still very limited, it is a little bit
more than just setting a sig_atomic_t and calling signal().
Be very, very careful trying to use library functions, file
i/o, memory allocation, or just about anything else inside a
signal handler invoked asynchronously (other than by a call to
raise()). The C++ library, the underlying C library, and
maybe even the operating system can be in a state where there
are severe limits on what they can do.
Yes. He really has to ask in a group specialized for his OS to
find out exactly what he can do. (The usual solution under Unix
is to run a special timer thread, and handle the signal
there---Posix allows a signal to unblock a normal thread, rather
than just invoke a signal handler, and you can then do just
about anything you could normally do in a thread.)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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