aboutsummaryrefslogtreecommitdiffstats
path: root/utils/signals/interrupts.cpp
diff options
context:
space:
mode:
Diffstat (limited to 'utils/signals/interrupts.cpp')
-rw-r--r--utils/signals/interrupts.cpp309
1 files changed, 309 insertions, 0 deletions
diff --git a/utils/signals/interrupts.cpp b/utils/signals/interrupts.cpp
new file mode 100644
index 000000000000..956a83c66802
--- /dev/null
+++ b/utils/signals/interrupts.cpp
@@ -0,0 +1,309 @@
+// Copyright 2012 The Kyua Authors.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright
+// notice, this list of conditions and the following disclaimer in the
+// documentation and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors
+// may be used to endorse or promote products derived from this software
+// without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "utils/signals/interrupts.hpp"
+
+extern "C" {
+#include <sys/types.h>
+
+#include <signal.h>
+#include <unistd.h>
+}
+
+#include <cstdlib>
+#include <cstring>
+#include <set>
+
+#include "utils/logging/macros.hpp"
+#include "utils/process/operations.hpp"
+#include "utils/sanity.hpp"
+#include "utils/signals/exceptions.hpp"
+#include "utils/signals/programmer.hpp"
+
+namespace signals = utils::signals;
+namespace process = utils::process;
+
+
+namespace {
+
+
+/// The interrupt signal that fired, or -1 if none.
+static volatile int fired_signal = -1;
+
+
+/// Collection of PIDs.
+typedef std::set< pid_t > pids_set;
+
+
+/// List of processes to kill upon reception of a signal.
+static pids_set pids_to_kill;
+
+
+/// Programmer status for the SIGHUP signal.
+static std::auto_ptr< signals::programmer > sighup_handler;
+/// Programmer status for the SIGINT signal.
+static std::auto_ptr< signals::programmer > sigint_handler;
+/// Programmer status for the SIGTERM signal.
+static std::auto_ptr< signals::programmer > sigterm_handler;
+
+
+/// Signal mask to restore after exiting a signal inhibited section.
+static sigset_t global_old_sigmask;
+
+
+/// Whether there is an interrupts_handler object in existence or not.
+static bool interrupts_handler_active = false;
+
+
+/// Whether there is an interrupts_inhibiter object in existence or not.
+static std::size_t interrupts_inhibiter_active = 0;
+
+
+/// Generic handler to capture interrupt signals.
+///
+/// From this handler, we record that an interrupt has happened so that
+/// check_interrupt() can know whether there execution has to be stopped or not.
+/// We also terminate any of our child processes (started by the
+/// utils::process::children class) so that any ongoing wait(2) system calls
+/// terminate.
+///
+/// \param signo The signal that caused this handler to be called.
+static void
+signal_handler(const int signo)
+{
+ static const char* message = "[-- Signal caught; please wait for "
+ "cleanup --]\n";
+ if (::write(STDERR_FILENO, message, std::strlen(message)) == -1) {
+ // We are exiting: the message printed here is only for informational
+ // purposes. If we fail to print it (which probably means something
+ // is really bad), there is not much we can do within the signal
+ // handler, so just ignore this.
+ }
+
+ fired_signal = signo;
+
+ for (pids_set::const_iterator iter = pids_to_kill.begin();
+ iter != pids_to_kill.end(); ++iter) {
+ process::terminate_group(*iter);
+ }
+}
+
+
+/// Installs signal handlers for potential interrupts.
+///
+/// \pre Must not have been called before.
+/// \post The various sig*_handler global variables are atomically updated.
+static void
+setup_handlers(void)
+{
+ PRE(sighup_handler.get() == NULL);
+ PRE(sigint_handler.get() == NULL);
+ PRE(sigterm_handler.get() == NULL);
+
+ // Create the handlers on the stack first so that, if any of them fails, the
+ // stack unwinding cleans things up.
+ std::auto_ptr< signals::programmer > tmp_sighup_handler(
+ new signals::programmer(SIGHUP, signal_handler));
+ std::auto_ptr< signals::programmer > tmp_sigint_handler(
+ new signals::programmer(SIGINT, signal_handler));
+ std::auto_ptr< signals::programmer > tmp_sigterm_handler(
+ new signals::programmer(SIGTERM, signal_handler));
+
+ // Now, update the global pointers, which is an operation that cannot fail.
+ sighup_handler = tmp_sighup_handler;
+ sigint_handler = tmp_sigint_handler;
+ sigterm_handler = tmp_sigterm_handler;
+}
+
+
+/// Uninstalls the signal handlers installed by setup_handlers().
+static void
+cleanup_handlers(void)
+{
+ sighup_handler->unprogram(); sighup_handler.reset(NULL);
+ sigint_handler->unprogram(); sigint_handler.reset(NULL);
+ sigterm_handler->unprogram(); sigterm_handler.reset(NULL);
+}
+
+
+
+/// Masks the signals installed by setup_handlers().
+///
+/// \param[out] old_sigmask The old signal mask to save via the
+/// \code oset \endcode argument with sigprocmask(2).
+static void
+mask_signals(sigset_t* old_sigmask)
+{
+ sigset_t mask;
+ sigemptyset(&mask);
+ sigaddset(&mask, SIGALRM);
+ sigaddset(&mask, SIGHUP);
+ sigaddset(&mask, SIGINT);
+ sigaddset(&mask, SIGTERM);
+ const int ret = ::sigprocmask(SIG_BLOCK, &mask, old_sigmask);
+ INV(ret != -1);
+}
+
+
+/// Resets the signal masking put in place by mask_signals().
+///
+/// \param[in] old_sigmask The old signal mask to restore via the
+/// \code set \endcode argument with sigprocmask(2).
+static void
+unmask_signals(sigset_t* old_sigmask)
+{
+ const int ret = ::sigprocmask(SIG_SETMASK, old_sigmask, NULL);
+ INV(ret != -1);
+}
+
+
+} // anonymous namespace
+
+
+/// Constructor that sets up the signal handlers.
+signals::interrupts_handler::interrupts_handler(void) :
+ _programmed(false)
+{
+ PRE(!interrupts_handler_active);
+ setup_handlers();
+ _programmed = true;
+ interrupts_handler_active = true;
+}
+
+
+/// Destructor that removes the signal handlers.
+///
+/// Given that this is a destructor and it can't report errors back to the
+/// caller, the caller must attempt to call unprogram() on its own.
+signals::interrupts_handler::~interrupts_handler(void)
+{
+ if (_programmed) {
+ LW("Destroying still-programmed signals::interrupts_handler object");
+ try {
+ unprogram();
+ } catch (const error& e) {
+ UNREACHABLE;
+ }
+ }
+}
+
+
+/// Unprograms all signals captured by the interrupts handler.
+///
+/// \throw system_error If the unprogramming of any signal fails.
+void
+signals::interrupts_handler::unprogram(void)
+{
+ PRE(_programmed);
+
+ // Modify the control variables first before unprogramming the handlers. If
+ // we fail to do the latter, we do not want to try again because we will not
+ // succeed (and we'll cause a crash due to failed preconditions).
+ _programmed = false;
+ interrupts_handler_active = false;
+
+ cleanup_handlers();
+ fired_signal = -1;
+}
+
+
+/// Constructor that sets up signal masking.
+signals::interrupts_inhibiter::interrupts_inhibiter(void)
+{
+ sigset_t old_sigmask;
+ mask_signals(&old_sigmask);
+ if (interrupts_inhibiter_active == 0) {
+ global_old_sigmask = old_sigmask;
+ }
+ ++interrupts_inhibiter_active;
+}
+
+
+/// Destructor that removes signal masking.
+signals::interrupts_inhibiter::~interrupts_inhibiter(void)
+{
+ if (interrupts_inhibiter_active > 1) {
+ --interrupts_inhibiter_active;
+ } else {
+ interrupts_inhibiter_active = false;
+ unmask_signals(&global_old_sigmask);
+ }
+}
+
+
+/// Checks if an interrupt has fired.
+///
+/// Calls to this function should be sprinkled in strategic places through the
+/// code protected by an interrupts_handler object.
+///
+/// Only one call to this function will raise an exception per signal received.
+/// This is to allow executing cleanup actions without reraising interrupt
+/// exceptions unless the user has fired another interrupt.
+///
+/// \throw interrupted_error If there has been an interrupt.
+void
+signals::check_interrupt(void)
+{
+ if (fired_signal != -1) {
+ const int original_fired_signal = fired_signal;
+ fired_signal = -1;
+ throw interrupted_error(original_fired_signal);
+ }
+}
+
+
+/// Registers a child process to be killed upon reception of an interrupt.
+///
+/// \pre Must be called with interrupts being inhibited. The caller must ensure
+/// that the call call to fork() and the addition of the PID happen atomically.
+///
+/// \param pid The PID of the child process. Must not have been yet regsitered.
+void
+signals::add_pid_to_kill(const pid_t pid)
+{
+ PRE(interrupts_inhibiter_active);
+ PRE(pids_to_kill.find(pid) == pids_to_kill.end());
+ pids_to_kill.insert(pid);
+}
+
+
+/// Unregisters a child process previously registered via add_pid_to_kill().
+///
+/// \pre Must be called with interrupts being inhibited. This is not necessary,
+/// but pushing this to the caller simplifies our logic and provides consistency
+/// with the add_pid_to_kill() call.
+///
+/// \param pid The PID of the child process. Must have been registered
+/// previously, and the process must have already been awaited for.
+void
+signals::remove_pid_to_kill(const pid_t pid)
+{
+ PRE(interrupts_inhibiter_active);
+ PRE(pids_to_kill.find(pid) != pids_to_kill.end());
+ pids_to_kill.erase(pid);
+}