Commit c00d5602 authored by Thomas Markwalder's avatar Thomas Markwalder
Browse files

[3407] Added on-receipt signal handling to util::SignalSet

util::SignalSet now supports registering a signal handler
from within it's internal handler.  This allows a custom
handler to process signals as soon as they occur, rather
than through deferred processing.
parent 7c4963ca
......@@ -48,29 +48,87 @@ std::list<int>* getSignalStates() {
/// @brief Internal signal handler for @c isc::util::io::SignalSet class.
/// This signal handler adds a signal number for which it is being
/// invoked to the queue of received signals. It prevents adding duplicated
/// signals. All duplicated signals are dropped. This prevents hammering
/// a process to invoke handlers (e.g. DHCP server reconfiguration), when
/// many the same signals are received one after another.
/// This handler catches all registered signals. When a signal arrives it
/// passes the signal to invokeOnReceiptHandler for "on-receipt" processing.
/// If this processing returns true if exists without further action,
/// otherwise it adds the signal number to the queue of received signals.
/// It prevents adding duplicated signals. All duplicated signals are dropped.
/// This prevents hammering a process to invoke handlers (e.g. DHCP server
/// reconfiguration), when many of the same signals are received one after
/// another.
/// @param sig Signal number.
void internalHandler(int sig) {
if (SignalSet::invokeOnReceiptHandler(sig)) {
// Signal has been handled by the on-receipt handler.
// Signal is using post-receipt handling, see if we've
// already received it.
std::list<int>* states = getSignalStates();
for (std::list<int>::const_iterator it = states->begin();
it != states->end(); ++it) {
if (sig == *it) {
it != states->end(); ++it) {
if (sig == *it) {
// First occurrence, so save it.
}; // end anon namespace
namespace isc {
namespace util {
const BoolSignalHandler SignalSet::EMPTY_BOOL_HANDLER = BoolSignalHandler();
BoolSignalHandler SignalSet::onreceipt_handler_ = EMPTY_BOOL_HANDLER;
SignalSet::invokeOnReceiptHandler(int sig) {
if (!SignalSet::onreceipt_handler_) {
return (false);
// First we set the signal to SIG_IGN. This causes any repeat occurrences
// to be discarded, not deferred as they would be if blocked. Note that
// we save the current sig action so we can restore it later.
struct sigaction sa;
struct sigaction prev_sa;
memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_IGN;
if (sigaction(sig, &sa, &prev_sa) < 0) {
// Highly unlikely we can get here.
const char* errmsg = strerror(errno);
isc_throw(SignalSetError, "failed to set SIG_IGN for signal "
<< sig << ": " << errmsg);
// Call the registered handler.
bool signal_processed = false;
try {
signal_processed = SignalSet::onreceipt_handler_(sig);
} catch (const std::exception& ex) {
// Restore the handler. We might fail to restore it, but we likely
// have bigger issues anyway.
sigaction(sig, &prev_sa, 0);
isc_throw(SignalSetError, "onreceipt_handler failed for signal "
<< sig << ": " << ex.what());
// Restore the sig action to reenable handling this signal.
if (sigaction(sig, &prev_sa, 0) < 0) {
// Highly unlikely we can get here.
const char* errmsg = strerror(errno);
isc_throw(SignalSetError, "failed to restore handler for signal "
<< sig << ": " << errmsg);
return (signal_processed);
SignalSet::SignalSet(const int sig0) {
......@@ -187,6 +245,7 @@ SignalSet::insert(const int sig) {
SignalSet::maskSignals(const int mask) const {
sigset_t new_set;
for (std::set<int>::const_iterator it = getRegisteredSignals()->begin();
it != getRegisteredSignals()->end(); ++it) {
sigaddset(&new_set, *it);
......@@ -225,5 +284,15 @@ SignalSet::remove(const int sig) {
SignalSet::setOnReceiptHandler(BoolSignalHandler handler) {
onreceipt_handler_ = handler;
SignalSet::clearOnReceiptHandler() {
onreceipt_handler_ = EMPTY_BOOL_HANDLER;
} // end of isc::util
} // end of isc
......@@ -40,26 +40,48 @@ typedef boost::shared_ptr<SignalSet> SignalSetPtr;
/// @brief Pointer to the signal handling function.
typedef boost::function<void(int signum)> SignalHandler;
/// @brief Pointer to a signal handling function which returns bool result.
/// The handler is expected to return true if the signal it was given has
/// been processed (i.e. should not be recorded for deferred processing) or
/// false in which case it will be recorded.
typedef boost::function<bool(int signum)> BoolSignalHandler;
/// @brief Represents a collection of signals handled in a customized way.
/// Kea processes must handle selected signals in a specialized way. For
/// example: SIGINT and SIGTERM must perform a graceful shut down of the
/// server. The SIGHUP signal is used to trigger server's reconfiguration.
/// This class allows specifying signals which should be handled in a
/// specialized way as well as specifying a signal handler function.
/// When a signal is received the signal handler function is called and
/// the code of the received signal is recorded. This function doesn't
/// do anything beyond recording the signal number to minimize the time
/// spent on handling the signal and process interruption. The process
/// can later check the signals received and call the handlers on its
/// descretion by calling a @c isc::util::io::SignalSet::handleNext function.
/// This class allows the caller to register one or more signals to catch
/// and process. Signals may be handled either immediately upon arrival and/or
/// recorded and processed later. To process signals immediately, the caller
/// must register an "on-receipt" handler. This handler is expected to return
/// a true or false indicating whether or not the signal has been processed.
/// Signal occurrences that are not processed by the on-receipt handler are
/// remembered by SignalSet for deferred processing. The caller can then query
/// SignalSet at their discretion to determine if any signal occurrences are
/// pending and process them.
/// SignalSet uses an internal handler to catch all registered signals. When
/// a signal arrives the internal handler will first attempt to invoke the
/// on-receipt handler. If one has been registered it is passed the
/// signal value as an argument and if it returns true upon completion, the
/// internal handler will exit without further action. If the on-receipt
/// handler returned false or one is not registered, then internal handler
/// will record the signal value for deferred processing. Note that once a
/// particular signal has been recorded, any further occurrences of that signal
/// will be discarded until the original occurrence has been processed. This
/// guards against rapid-fire occurrences of the same signal.
/// @note This class is not thread safe. It uses static variables and
/// functions to track a global state of signal registration and received
/// signals' queue.
class SignalSet : public boost::noncopyable {
/// @brief Optional handler to execute at the time of signal receipt
static BoolSignalHandler onreceipt_handler_;
static const BoolSignalHandler EMPTY_BOOL_HANDLER;
/// @brief Constructor installing one signal.
......@@ -128,6 +150,38 @@ public:
/// @param sig A code of the signal to be removed.
void remove(const int sig);
/// @brief Registers a handler as the onreceipt signal handler
/// Sets the given handler as the handler to invoke immediately
/// upon receipt of a a registered signal.
/// @note Currently, the on-receipt handler is stored as a static
/// value and hence there may only be one such handler at a time
/// for a given process.
/// @param handler the signal handler to register
static void setOnReceiptHandler(BoolSignalHandler handler);
/// @brief Unregeisters the onreceipt signal handler
static void clearOnReceiptHandler();
/// @brief Invokes the onreceipt handler if it exists
/// This static method is used by @c isc::util::io::SignalSet class to
/// invoke the registered handler (if one) immediately upon receipt of
/// a registered signal.
/// Prior to invoking the handler, it sets signal action for the given
/// signal to SIG_IGN which prevents any repeat signal occurences from
/// queuing while the handler is executing. Upon completion of the handler,
/// the signal action is restored which reenables receipt and handling of
/// the signal.
/// @param sig Signal number.
/// @return Boolean false if no on-receipt handler was registered,
/// otherwise it is the value returned by the on-receipt handler.
static bool invokeOnReceiptHandler(int sig);
/// @brief Blocks signals in the set.
......@@ -178,6 +232,7 @@ private:
/// @brief Stores the set of signals registered in this signal set.
std::set<int> local_signals_;
......@@ -37,7 +37,8 @@ public:
/// signal handler function.
: signal_set_(),
secondary_signal_set_() {
onreceipt_trues_(0) {
handler_calls_ = 0;
signum_ = -1;
......@@ -54,7 +55,7 @@ public:
/// @brief Signal handler used by unit tests.
/// @brief Deferred processing signal handler used by unit tests.
/// @param signum Signal being handled.
static void testHandler(int signum) {
......@@ -62,6 +63,22 @@ public:
/// @brief Immediate processing signal handler used by unit tests.
/// The handler processes only SIGHUP. All others will pass through.
/// @param signum Signal being handled.
/// @return Boolean true if the handler has processed the signal, false
/// otherwise.
bool onReceiptHandler(int signum) {
if (signum == SIGHUP) {
return (true);
return (false);
/// @brief Number of handler calls so far.
static int handler_calls_;
/// @brief The last signal handled.
......@@ -70,6 +87,8 @@ public:
SignalSetPtr signal_set_;
/// @brief Second signal set object.
SignalSetPtr secondary_signal_set_;
/// @brief Number of true returns from onReceiptHandler so far.
int onreceipt_trues_;
int SignalSetTest::handler_calls_ = 0;
......@@ -184,5 +203,47 @@ TEST_F(SignalSetTest, duplicates) {
EXPECT_THROW(other->add(SIGHUP), SignalSetError);
/// Check that on-receipt processing works.
TEST_F(SignalSetTest, onReceiptTests) {
// Install an on-receipt handler.
this, _1));
// Create a SignalSet for SIGHUP and SIGUSR1.
ASSERT_NO_THROW(signal_set_.reset(new SignalSet(SIGHUP, SIGUSR1)));
// Generate SIGHUP, which the on-receipt handler should process.
// Verify that the on-receipt handler processed the signal and that
// no signals are pending.
ASSERT_EQ(0, raise(SIGHUP));
EXPECT_EQ(1, onreceipt_trues_);
EXPECT_EQ(-1, signal_set_->getNext());
// Generate SIGHUP, which the on-receipt handler should NOT process.
// Verify the on-receipt handler did not the signal and that SIGUSR1
// is pending.
ASSERT_EQ(0, raise(SIGUSR1));
EXPECT_EQ(1, onreceipt_trues_);
EXPECT_EQ(SIGUSR1, signal_set_->getNext());
// Verify we can process SIGUSR1 with the deferred handler.
signal_set_->handleNext(boost::bind(&SignalSetTest::testHandler, _1));
EXPECT_EQ(1, handler_calls_);
EXPECT_EQ(SIGUSR1, signum_);
// Unregister the on-receipt handler.
// Generate SIGHUP.
// Verify that the on-receipt handler did not process the signal, and
// that SIGHUP is pending.
ASSERT_EQ(0, raise(SIGHUP));
EXPECT_EQ(1, onreceipt_trues_);
EXPECT_EQ(SIGHUP, signal_set_->getNext());
// Verify we can process it with deferred handler.
signal_set_->handleNext(boost::bind(&SignalSetTest::testHandler, _1));
EXPECT_EQ(2, handler_calls_);
} // end of anonymous namespace
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