1// Copyright 2010 The Kyua Authors.
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28
29#include "utils/signals/programmer.hpp"
30
31extern "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/noncopyable.hpp"
40#include "utils/sanity.hpp"
41#include "utils/signals/exceptions.hpp"
42
43
44namespace utils {
45namespace signals {
46
47
48/// Internal implementation for the signals::programmer class.
49struct programmer::impl : utils::noncopyable {
50    /// The number of the signal managed by this programmer.
51    int signo;
52
53    /// Whether the signal is currently programmed by us or not.
54    bool programmed;
55
56    /// The signal handler that we replaced; to be restored on unprogramming.
57    struct ::sigaction old_sa;
58
59    /// Initializes the internal implementation of the programmer.
60    ///
61    /// \param signo_ The signal number.
62    impl(const int signo_) :
63        signo(signo_),
64        programmed(false)
65    {
66    }
67};
68
69
70} // namespace signals
71} // namespace utils
72
73
74namespace signals = utils::signals;
75
76
77/// Programs a signal handler.
78///
79/// \param signo The signal for which to install the handler.
80/// \param handler The handler to install.
81///
82/// \throw signals::system_error If there is an error programming the signal.
83signals::programmer::programmer(const int signo, const handler_type handler) :
84    _pimpl(new impl(signo))
85{
86    struct ::sigaction sa;
87    sa.sa_handler = handler;
88    sigemptyset(&sa.sa_mask);
89    sa.sa_flags = SA_RESTART;
90
91    if (::sigaction(_pimpl->signo, &sa, &_pimpl->old_sa) == -1) {
92        const int original_errno = errno;
93        throw system_error(F("Could not install handler for signal %s") %
94                           _pimpl->signo, original_errno);
95    } else
96        _pimpl->programmed = true;
97}
98
99
100/// Destructor; unprograms the signal handler if still programmed.
101///
102/// Given that this is a destructor and it can't report errors back to the
103/// caller, the caller must attempt to call unprogram() on its own.
104signals::programmer::~programmer(void)
105{
106    if (_pimpl->programmed) {
107        LW("Destroying still-programmed signals::programmer object");
108        try {
109            unprogram();
110        } catch (const system_error& e) {
111            UNREACHABLE;
112        }
113    }
114}
115
116
117/// Unprograms the signal handler.
118///
119/// \pre The signal handler is programmed (i.e. this can only be called once).
120///
121/// \throw system_error If unprogramming the signal failed.  If this happens,
122///     the signal is left programmed, this object forgets about the signal and
123///     therefore there is no way to restore the original handler.
124void
125signals::programmer::unprogram(void)
126{
127    PRE(_pimpl->programmed);
128
129    // If we fail, we don't want the destructor to attempt to unprogram the
130    // handler again, as it would result in a crash.
131    _pimpl->programmed = false;
132
133    if (::sigaction(_pimpl->signo, &_pimpl->old_sa, NULL) == -1) {
134        const int original_errno = errno;
135        throw system_error(F("Could not reset handler for signal %s") %
136                           _pimpl->signo, original_errno);
137    }
138}
139