Add experimental Linux shared-memory IPC transport

CMakeLists.txt

@@ -991,6 +991,8 @@ set(cxx-sources
     select.cpp
     server.cpp
     session_base.cpp
+    shm_engine.cpp
+    shm_state.cpp
     signaler.cpp
     socket_base.cpp
     socks.cpp
@@ -1126,6 +1128,11 @@ set(cxx-sources
     select.hpp
     server.hpp
     session_base.hpp
+    shm_channel.hpp
+    shm_engine.hpp
+    shm_fd.hpp
+    shm_ring.hpp
+    shm_state.hpp
     signaler.hpp
     socket_base.hpp
     socket_poller.hpp
@@ -1620,6 +1627,9 @@ if(BUILD_SHARED)
       inproc_lat
       inproc_thr
       proxy_thr)
+  if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+    list(APPEND perf-tools shm_pair_thr)
+  endif()
 
   if(NOT CMAKE_BUILD_TYPE STREQUAL "Debug") # Why?
     option(WITH_PERF_TOOL "Build with perf-tools" ON)

Makefile.am

@@ -193,6 +193,13 @@ src_libzmq_la_SOURCES = \
 	src/server.hpp \
 	src/session_base.cpp \
 	src/session_base.hpp \
+	src/shm_channel.hpp \
+	src/shm_engine.cpp \
+	src/shm_engine.hpp \
+	src/shm_fd.hpp \
+	src/shm_ring.hpp \
+	src/shm_state.cpp \
+	src/shm_state.hpp \
 	src/signaler.cpp \
 	src/signaler.hpp \
 	src/socket_base.cpp \
@@ -397,6 +404,11 @@ noinst_PROGRAMS = \
 	perf/inproc_thr \
 	perf/proxy_thr
 
+if ON_LINUX
+noinst_PROGRAMS += \
+	perf/shm_pair_thr
+endif
+
 perf_local_lat_LDADD = src/libzmq.la
 perf_local_lat_SOURCES = perf/local_lat.cpp
 
@@ -418,6 +430,9 @@ perf_inproc_thr_SOURCES = perf/inproc_thr.cpp
 perf_proxy_thr_LDADD = src/libzmq.la
 perf_proxy_thr_SOURCES = perf/proxy_thr.cpp
 
+perf_shm_pair_thr_LDADD = src/libzmq.la
+perf_shm_pair_thr_SOURCES = perf/shm_pair_thr.cpp
+
 if ENABLE_STATIC
 noinst_PROGRAMS += \
 	perf/benchmark_radix_tree
@@ -1010,12 +1025,28 @@ tests_test_security_gssapi_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
 endif
 
 if ON_LINUX
-test_apps += tests/test_abstract_ipc
+test_apps += \
+	tests/test_abstract_ipc \
+	tests/test_pair_shm \
+	tests/test_shm_channel \
+	tests/test_shm_ring
 
 tests_test_abstract_ipc_SOURCES = tests/test_abstract_ipc.cpp
 tests_test_abstract_ipc_LDADD = ${TESTUTIL_LIBS} src/libzmq.la
 tests_test_abstract_ipc_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
 
+tests_test_pair_shm_SOURCES = tests/test_pair_shm.cpp
+tests_test_pair_shm_LDADD = ${TESTUTIL_LIBS} src/libzmq.la
+tests_test_pair_shm_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
+
+tests_test_shm_channel_SOURCES = tests/test_shm_channel.cpp
+tests_test_shm_channel_LDADD = ${TESTUTIL_LIBS} src/libzmq.la
+tests_test_shm_channel_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
+
+tests_test_shm_ring_SOURCES = tests/test_shm_ring.cpp
+tests_test_shm_ring_LDADD = ${TESTUTIL_LIBS} src/libzmq.la
+tests_test_shm_ring_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
+
 # TODO: gets stuck even with long timeout running under Github Actions
 if !VALGRIND_ENABLED
 test_apps += tests/test_socks

include/zmq.h

@@ -237,6 +237,10 @@ ZMQ_EXPORT int zmq_msg_init (zmq_msg_t *msg_);
 ZMQ_EXPORT int zmq_msg_init_size (zmq_msg_t *msg_, size_t size_);
 ZMQ_EXPORT int zmq_msg_init_data (
   zmq_msg_t *msg_, void *data_, size_t size_, zmq_free_fn *ffn_, void *hint_);
+ZMQ_EXPORT int
+zmq_shm_msg_init (void *s_, zmq_msg_t *msg_, size_t size_);
+ZMQ_EXPORT int
+zmq_shm_msg_send (zmq_msg_t *msg_, void *s_, int flags_);
 ZMQ_EXPORT int zmq_msg_send (zmq_msg_t *msg_, void *s_, int flags_);
 ZMQ_EXPORT int zmq_msg_recv (zmq_msg_t *msg_, void *s_, int flags_);
 ZMQ_EXPORT int zmq_msg_close (zmq_msg_t *msg_);
@@ -353,6 +357,7 @@ ZMQ_EXPORT const char *zmq_msg_gets (const zmq_msg_t *msg_,
 /*  Message options                                                           */
 #define ZMQ_MORE 1
 #define ZMQ_SHARED 3
+#define ZMQ_SHM 4
 
 /*  Send/recv options.                                                        */
 #define ZMQ_DONTWAIT 1