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     28 
     29 #include "utils/signals/programmer.hpp"
     30 
     31 extern "C" {
     32 #include <signal.h>
     33 }
     34 
     35 #include <cerrno>
     36 
     37 #include "utils/format/macros.hpp"
     38 #include "utils/logging/macros.hpp"
     39 #include "utils/sanity.hpp"
     40 #include "utils/signals/exceptions.hpp"
     41 
     42 
     43 namespace utils {
     44 namespace signals {
     45 
     46 
     47 /// Internal implementation for the signals::programmer class.
     48 struct programmer::impl {
     49     /// The number of the signal managed by this programmer.
     50     int signo;
     51 
     52     /// Whether the signal is currently programmed by us or not.
     53     bool programmed;
     54 
     55     /// The signal handler that we replaced; to be restored on unprogramming.
     56     struct ::sigaction old_sa;
     57 
     58     /// Initializes the internal implementation of the programmer.
     59     ///
     60     /// \param signo_ The signal number.
     61     impl(const int signo_) :
     62         signo(signo_),
     63         programmed(false)
     64     {
     65     }
     66 };
     67 
     68 
     69 } // namespace signals
     70 } // namespace utils
     71 
     72 
     73 namespace signals = utils::signals;
     74 
     75 
     76 /// Programs a signal handler.
     77 ///
     78 /// \param signo The signal for which to install the handler.
     79 /// \param handler The handler to install.
     80 ///
     81 /// \throw signals::system_error If there is an error programming the signal.
     82 signals::programmer::programmer(const int signo, const handler_type handler) :
     83     _pimpl(new impl(signo))
     84 {
     85     struct ::sigaction sa;
     86     sa.sa_handler = handler;
     87     sigemptyset(&sa.sa_mask);
     88     sa.sa_flags = SA_RESTART;
     89 
     90     if (::sigaction(_pimpl->signo, &sa, &_pimpl->old_sa) == -1) {
     91         const int original_errno = errno;
     92         throw system_error(F("Could not install handler for signal %s") %
     93                            _pimpl->signo, original_errno);
     94     } else
     95         _pimpl->programmed = true;
     96 }
     97 
     98 
     99 /// Destructor; unprograms the signal handler if still programmed.
    100 ///
    101 /// Given that this is a destructor and it can't report errors back to the
    102 /// caller, the caller must attempt to call unprogram() on its own.
    103 signals::programmer::~programmer(void)
    104 {
    105     if (_pimpl->programmed) {
    106         LW("Destroying still-programmed signals::programmer object");
    107         try {
    108             unprogram();
    109         } catch (const system_error& e) {
    110             UNREACHABLE;
    111         }
    112     }
    113 }
    114 
    115 
    116 /// Unprograms the signal handler.
    117 ///
    118 /// \pre The signal handler is programmed (i.e. this can only be called once).
    119 ///
    120 /// \throw system_error If unprogramming the signal failed.  If this happens,
    121 ///     the signal is left programmed, this object forgets about the signal and
    122 ///     therefore there is no way to restore the original handler.
    123 void
    124 signals::programmer::unprogram(void)
    125 {
    126     PRE(_pimpl->programmed);
    127 
    128     // If we fail, we don't want the destructor to attempt to unprogram the
    129     // handler again, as it would result in a crash.
    130     _pimpl->programmed = false;
    131 
    132     if (::sigaction(_pimpl->signo, &_pimpl->old_sa, NULL) == -1) {
    133         const int original_errno = errno;
    134         throw system_error(F("Could not reset handler for signal %s") %
    135                            _pimpl->signo, original_errno);
    136     }
    137 }
    138