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libkqueue

CI Linux CI Windows Test suite FreeBSD Test suite macOS Coverity

A user space implementation of the kqueue(2) kernel event notification mechanism libkqueue acts as a translator between the kevent structure and the native kernel facilities on Linux, Android, Solaris, and Windows.

libkqueue is not perfect, and you may need to change the behaviour of your application to work around limitations on a given platform. Please see BUGS for known behavioural differences between libkqueue and BSD kqueues.

Supported Event Types

  • vnode
  • socket
  • proc
  • user
  • timer

Installation - Linux, Solaris

cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib <path to source>
make
make install

Installation - Red Hat

cmake3 -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib <path to source>
make
cpack3 -G RPM

Installation - Debian

cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib <path to source>
make
cpack -G DEB

Installation - Android

cmake -G "Unix Makefiles" -DCMAKE_C_COMPILER=<path to NDK compiler> -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib <path to source>
make

Windows (Visual Studio Project)

cmake -G "Visual Studio 14 2015" <path to source>
cmake --build .

Windows (clang/C2) (Visual Studio Project)

cmake -G "Visual Studio 14 2015" -T "LLVM-vs2014" <path to source>
cmake --build .

Windows (cross-compiling on Ubuntu using MinGW)

sudo apt-get install mingw-w64
rm -rf CMakeCache.txt CMakeFiles
mkdir build
cd build
cmake -DCMAKE_TOOLCHAIN_FILE=Toolchain-mingw32.cmake ..
make

Xcode (project)

cmake -G "Xcode" <path to source>

Source archive

mkdir -p cmake-build-source
cd cmake-build-source
cmake ..
make package_source

Running Unit Tests

cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib -DENABLE_TESTING=YES -DCMAKE_BUILD_TYPE=Debug <path to source>
make
make test

Build & Running only the test suite

Helpful to see the behavior of the tests on systems with native kqueue, e.g: macOS, FreeBSD

cd test
cmake .
make
./libkqueue-test

To enable tests which expose bugs in native kqueue implementations pass -DWITH_NATIVE_KQUEUE_BUGS=1 to cmake. i.e. cmake . test/CMakeLists.txt -DWITH_NATIVE_KQUEUE_BUGS=1.

Debugging

For best results add -DCMAKE_BUILD_TYPE=Debug to your cmake invocation, this will disable optimisation and add debugging symbols to ensure your debugger produces usable output, it also enables asserts.

The environmental variable KQUEUE_DEBUG can then be set to enable debug output from libkqueue and the test utility.

KQUEUE_DEBUG=1 <your application>

When building under clang and some later versions of GCC, you can add the following flags:

  • -DENABLE_ASAN=YES, enables address sansitizer (detects use after free issues, and out of bounds accesses).
  • -DENABLE_LSAN=YES, enables leak sanitizer (detects memory leaks).
  • -DENABLE_TSAN=YES, enables thread sanitizer (detects races).
  • -DENABLE_UBSAN=YES, enables undefined behaviour sanitizer (detects misaligned accesses, integer wrap, divide by zero etc...).

libkqueue filter

The libkqueue filter EVFILT_LIBKQUEUE exposes runtime configuration options and data. When querying/configuring libkqueue using EVFILT_LIBKQUEUE the flags field should be set to EV_ADD, and the fflags field should be one of the following:

  • NOTE_VERSION return the current version as a 32bit unsigned integer in the format MMmmpprr (Major, minor, patch, release) in the data field of an entry in the eventlist.

  • NOTE_VERSION_STR return the current version as a string in the udata field of an entry in the eventlist.

  • NOTE_THREAD_SAFE defaults to on (1).

    • If the data field is 0 the global mutex will not be locked after resolving a kqueue fd to a kqueue structure. The application must guarantee any given kqueue will be created and destroyed by the same thread.
    • If the data field is 1 kqueues can be created and destroyed in different threads safely. This may add contention around the global mutex.

  • NOTE_FORK_CLEANUP defaults to on (1).

    • If the data field is 0 no resources will be cleaned up on fork.
    • if the data field is 1 all kqueues will be closed/freed on fork.

    The default behaviour matches native kqueue but may be expensive if many kqueues are active. If EV_RECEIPT is set, the previous value of cleanup flag will be provided in a receipt event.

Example - retrieving version string:

struct kevent kev, receipt;

EV_SET(&kev, 0, EVFILT_LIBKQUEUE, EV_ADD, NOTE_VERSION_STR, 0, NULL);
if (kevent(kqfd, &kev, 1, &receipt, 1, &(struct timespec){}) != 1) {
    //error
}
printf("libkqueue version - %s", (char *)receipt.udata);

The following are only available in debugging builds of libkqueue:

  • NOTE_DEBUG defaults to off 0, but may be overridden by the environmental variable KQUEUE_DEBUG.

    • If the data field is 0 no debug messages will be produced.
    • If the data field is 1 debug messages will be produced.

    If EV_RECEIPT is set the previous value of debug flag will be provided in a receipt event.

  • NOTE_DEBUG_PREFIX defaults to KQ. Logging prefix will be set to the value of a string pointed to by the data field. Logging prefix strings will be memdup'd.

  • NOTE_DEBUG_FUNC defaults to a function which writes debug information to stderr. The data field should contain a pointer to a function with the signature void (*debug_func)(char const *fmt, ...), or NULL to restore to original logging function.

Building Applications

CFLAGS += -I/usr/include/kqueue
LDFLAGS += -lkqueue

Tutorials & Examples

Kqueues for Fun and Profit

Handling TCP Connections with Kqueue Event Notification

Releases History

See the ChangeLog.