SignalHandler.cc

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// -*- mode: c++; c-basic-offset:4 -*-
 
// This file is part of libdap, A C++ implementation of the OPeNDAP Data
// Access Protocol.
 
// Copyright (c) 2002,2003 OPeNDAP, Inc.
// Author: James Gallagher <jgallagher@opendap.org>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
//
// You can contact OPeNDAP, Inc. at PO Box 112, Saunderstown, RI. 02874-0112.
 
// (c) COPYRIGHT URI/MIT 1994-2002
// Please read the full copyright statement in the file COPYRIGHT_URI.
//
// Authors:
//      jhrg,jimg       James Gallagher <jgallagher@gso.uri.edu>
 
#include "config.h"
 
#include <csignal>
 
#include "SignalHandler.h"
#include "util.h"
 
namespace libdap {
 
std::vector<EventHandler *> SignalHandler::d_signal_handlers{NSIG, nullptr};
std::vector<Sigfunc *> SignalHandler::d_old_handlers{NSIG, nullptr};

void SignalHandler::dispatcher(int signum) {
    // Perform a sanity check...
    if (d_signal_handlers[signum] != nullptr)
        // Dispatch the handler's hook method.
        d_signal_handlers[signum]->handle_signal(signum);
 
    Sigfunc *old_handler = SignalHandler::d_old_handlers[signum];
    if (old_handler == SIG_IGN || old_handler == SIG_ERR)
        return;
    else if (old_handler == SIG_DFL)
        throw Error(internal_error, "Signal handler operation on an unsupported signal.");
    else
        old_handler(signum);
}

SignalHandler *SignalHandler::instance() {
    static SignalHandler instance;
    return &instance;
}

EventHandler *SignalHandler::register_handler(int signum, EventHandler *eh, bool ignore_by_default) {
    // Check first for improper use.
    switch (signum) {
#ifndef WIN32
    case SIGHUP:
    case SIGKILL:
    case SIGUSR1:
    case SIGUSR2:
    case SIGPIPE:
    case SIGALRM:
#endif
    case SIGINT:
    case SIGTERM:
        break;
 
    default:
        throw InternalErr(__FILE__, __LINE__,
                          string("Call to register_handler with unsupported signal (") + long_to_string(signum) +
                              string(")."));
    }
 
    // Save the old EventHandler
    EventHandler *old_eh = SignalHandler::d_signal_handlers[signum];
 
    SignalHandler::d_signal_handlers[signum] = eh;
 
    // Register the dispatcher to handle this signal. See Stevens, Advanced
    // Programming in the UNIX Environment, p.298.
#ifndef WIN32
    struct sigaction sa {};
    sa.sa_handler = dispatcher;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
 
    // Try to suppress restarting system calls if we're handling an alarm.
    // This lets alarms block I/O calls that would normally restart. 07/18/03
    // jhrg
    if (signum == SIGALRM) {
#ifdef SA_INTERUPT
        sa.sa_flags |= SA_INTERUPT;
#endif
    } else {
#ifdef SA_RESTART
        sa.sa_flags |= SA_RESTART;
#endif
    }
 
    struct sigaction old_sa {}; // extract the old handler/action
 
    if (sigaction(signum, &sa, &old_sa) < 0)
        throw InternalErr(__FILE__, __LINE__, "Could not register a signal handler.");
 
    // Take care of the case where this interface is used to register a
    // handler more than once. We want to make sure that the dispatcher is
    // not installed as the 'old handler' because that results in an infinite
    // loop. 02/10/04 jhrg
    if (ignore_by_default)
        SignalHandler::d_old_handlers[signum] = SIG_IGN;
    else if (old_sa.sa_handler != &dispatcher)
        SignalHandler::d_old_handlers[signum] = old_sa.sa_handler;
#endif // ndef WIN32
 
    return old_eh;
}

EventHandler *SignalHandler::remove_handler(int signum) {
    EventHandler *old_eh = SignalHandler::d_signal_handlers[signum];
 
    SignalHandler::d_signal_handlers[signum] = nullptr;
 
    return old_eh;
}
 
} // namespace libdap