Problem: selection of condition_variable_t implementation is confusing and not configurable

Solution: move configuration to build definition

CMakeLists.txt

@@ -250,6 +250,7 @@ include(CheckCSourceRuns)
 include(CMakeDependentOption)
 include(CheckCXXSymbolExists)
 include(CheckSymbolExists)
+include(FindThreads)
 
 execute_process(COMMAND getconf LEVEL1_DCACHE_LINESIZE OUTPUT_VARIABLE CACHELINE_SIZE ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
 if(CACHELINE_SIZE STREQUAL "" OR CACHELINE_SIZE EQUAL 0 OR CACHELINE_SIZE EQUAL -1)
@@ -307,6 +308,43 @@ if (WIN32)
     add_definitions(-D_WIN32_WINNT=${ZMQ_WIN32_WINNT})
 endif(WIN32)
 
+###################### BEGIN condition_variable_t selection
+if(NOT ZMQ_CV_IMPL)
+    # prefer C++11 STL std::condition_variable implementation, if available
+    check_include_files(condition_variable ZMQ_HAVE_STL_CONDITION_VARIABLE LANGUAGE CXX)
+
+    if (ZMQ_HAVE_STL_CONDITION_VARIABLE)
+        set(ZMQ_CV_IMPL_DEFAULT "stl11")
+    else()
+        if(WIN32 AND NOT CMAKE_SYSTEM_VERSION VERSION_LESS "6.0")
+            # Win32API CONDITION_VARIABLE is supported from Windows Vista only
+            set(ZMQ_CV_IMPL_DEFAULT "win32api")
+        elseif(CMAKE_USE_PTHREADS_INIT)
+            set(ZMQ_CV_IMPL_DEFAULT "pthreads")
+        else()
+            set(ZMQ_CV_IMPL_DEFAULT "none")
+        endif()
+    endif()
+
+    # TODO a vxworks implementation also exists, but vxworks is not currently supported with cmake at all
+    set(ZMQ_CV_IMPL "${ZMQ_CV_IMPL_DEFAULT}" CACHE STRING "Choose condition_variable_t implementation. Valid values are
+       stl11, win32api, pthreads, none [default=autodetect]")
+endif()
+
+message(STATUS "Using condition_variable_t implementation: ${ZMQ_CV_IMPL}")
+if(ZMQ_CV_IMPL STREQUAL "stl11")
+    set(ZMQ_USE_CV_IMPL_STL11 1)
+elseif(ZMQ_CV_IMPL STREQUAL "win32api")
+    set(ZMQ_USE_CV_IMPL_WIN32API 1)
+elseif(ZMQ_CV_IMPL STREQUAL "pthreads")
+    set(ZMQ_USE_CV_IMPL_PTHREADS 1)
+elseif(ZMQ_CV_IMPL STREQUAL "none")
+    set(ZMQ_USE_CV_IMPL_NONE 1)
+else()
+    message(ERROR "Unknown value for ZMQ_CV_IMPL: ${ZMQ_CV_IMPL}")
+endif()
+###################### END condition_variable_t selection
+
 if(CMAKE_SYSTEM_NAME STREQUAL "WindowsStore" AND CMAKE_SYSTEM_VERSION STREQUAL "10.0")
   set(ZMQ_HAVE_WINDOWS_UWP ON)
 endif()

acinclude.m4

@@ -1189,3 +1189,44 @@ AC_DEFUN([LIBZMQ_CHECK_CACHELINE], [{
 	AC_MSG_NOTICE([Using "$zmq_cacheline_size" bytes alignment for lock-free data structures])
 	AC_DEFINE_UNQUOTED(ZMQ_CACHELINE_SIZE, $zmq_cacheline_size, [Using "$zmq_cacheline_size" bytes alignment for lock-free data structures])
 }])
+
+dnl ################################################################################
+dnl # LIBZMQ_CHECK_CV_IMPL([action-if-found], [action-if-not-found])               #
+dnl # Choose condition variable implementation                                     #
+dnl ################################################################################
+
+AC_DEFUN([LIBZMQ_CHECK_CV_IMPL], [{
+    # Allow user to override condition variable autodetection
+    AC_ARG_WITH([cv-impl],
+        [AS_HELP_STRING([--with-cv-impl],
+        [choose condition variable implementation manually. Valid values are 'stl11', 'pthread', 'none', or 'auto'. [default=auto]])])
+
+    if test "x$with_cv_impl" == "x"; then
+        cv_impl=auto
+    else
+        cv_impl=$with_cv_impl
+    fi
+    case $host_os in
+      vxworks*)
+        cv_impl="vxworks"
+        AC_DEFINE(ZMQ_USE_CV_IMPL_VXWORKS, 1, [Use vxworks condition variable implementation.])
+      ;;
+    esac
+    if test "$cv_impl" == "auto" || test "$cv_impl" == "stl11"; then
+        AC_LANG_PUSH([C++])
+        AC_CHECK_HEADERS(condition_variable, [stl11="yes"
+            AC_DEFINE(ZMQ_USE_CV_IMPL_STL11, 1, [Use stl11 condition variable implementation.])],
+            [stl11="no"])
+        AC_LANG_POP([C++])
+        if test "$cv_impl" == "stl11" && test "x$stl11" == "xno"; then
+            AC_MSG_ERROR([--with-cv-impl set to stl11 but cannot find condition_variable])
+        fi
+    fi
+    if test "$cv_impl" == "pthread" || test "x$stl11" == "xno"; then
+        AC_DEFINE(ZMQ_USE_CV_IMPL_PTHREADS, 1, [Use pthread condition variable implementation.])
+    fi
+    if test "$cv_impl" == "none"; then
+        AC_DEFINE(ZMQ_USE_CV_IMPL_NONE, 1, [Use no condition variable implementation.])
+    fi
+       AC_MSG_NOTICE([Using "$cv_impl" condition variable implementation.])
+}])

builds/cmake/platform.hpp.in

 #ifndef __ZMQ_PLATFORM_HPP_INCLUDED__
 #define __ZMQ_PLATFORM_HPP_INCLUDED__
 
+#cmakedefine ZMQ_USE_CV_IMPL_STL11
+#cmakedefine ZMQ_USE_CV_IMPL_WIN32API
+#cmakedefine ZMQ_USE_CV_IMPL_PTHREADS
+#cmakedefine ZMQ_USE_CV_IMPL_NONE
+
 #cmakedefine ZMQ_IOTHREAD_POLLER_USE_KQUEUE
 #cmakedefine ZMQ_IOTHREAD_POLLER_USE_EPOLL
 #cmakedefine ZMQ_IOTHREAD_POLLER_USE_EPOLL_CLOEXEC

configure.ac

@@ -381,6 +381,9 @@ LIBZMQ_CHECK_POLLER
 # Check cacheline size, set appropriate macro in src/platform.hpp
 LIBZMQ_CHECK_CACHELINE
 
+# Check condition variable implementation, set appropriate macro in src/platform.hpp
+LIBZMQ_CHECK_CV_IMPL
+
 # Checks for header files.
 AC_HEADER_STDC
 AC_CHECK_HEADERS(\

src/condition_variable.hpp

@@ -35,25 +35,7 @@
 
 //  Condition variable class encapsulates OS mutex in a platform-independent way.
 
-#ifdef ZMQ_HAVE_WINDOWS
-
-#include "windows.hpp"
-#if defined(_MSC_VER)
-#if _MSC_VER >= 1800
-#define _SUPPORT_CONDITION_VARIABLE 1
-#else
-#define _SUPPORT_CONDITION_VARIABLE 0
-#endif
-#else
-#if _cplusplus >= 201103L
-#define _SUPPORT_CONDITION_VARIABLE 1
-#else
-#define _SUPPORT_CONDITION_VARIABLE 0
-#endif
-#endif
-
-// Condition variable is supported from Windows Vista only, to use condition variable define _WIN32_WINNT to 0x0600
-#if _WIN32_WINNT < 0x0600 && !_SUPPORT_CONDITION_VARIABLE
+#if defined(ZMQ_USE_CV_IMPL_NONE)
 
 namespace zmq
 {
@@ -79,16 +61,12 @@ class condition_variable_t
 };
 }
 
-#else
+#elif defined(ZMQ_USE_CV_IMPL_WIN32API)
 
-#if _SUPPORT_CONDITION_VARIABLE || defined(ZMQ_HAVE_WINDOWS_TARGET_XP)
-#include <condition_variable>
-#endif
+#include "windows.hpp"
 
 namespace zmq
 {
-
-#if !defined(ZMQ_HAVE_WINDOWS_TARGET_XP) && _WIN32_WINNT >= 0x0600
 class condition_variable_t
 {
   public:
@@ -121,7 +99,14 @@ class condition_variable_t
     condition_variable_t (const condition_variable_t &);
     void operator= (const condition_variable_t &);
 };
-#else
+}
+
+#elif defined(ZMQ_USE_CV_IMPL_STL11)
+
+#include <condition_variable>
+
+namespace zmq
+{
 class condition_variable_t
 {
   public:
@@ -158,13 +143,9 @@ class condition_variable_t
     condition_variable_t (const condition_variable_t &);
     void operator= (const condition_variable_t &);
 };
-
-#endif
 }
 
-#endif
-
-#elif defined ZMQ_HAVE_VXWORKS
+#elif defined(ZMQ_USE_CV_IMPL_VXWORKS)
 
 #include <sysLib.h>
 
@@ -248,7 +229,8 @@ class condition_variable_t
     const condition_variable_t &operator= (const condition_variable_t &);
 };
 }
-#else
+
+#elif defined(ZMQ_USE_CV_IMPL_PTHREADS)
 
 #include <pthread.h>
 
@@ -344,5 +326,4 @@ class condition_variable_t
 
 #endif
 
-
 #endif