Ticket #68716: patch-have_shared_mutex.diff

cmake/template/cpl_config.h.in

@@ -175 +175 @@
 /* Define to 1 if you have the `sched_getaffinity' function. */
 #cmakedefine HAVE_SCHED_GETAFFINITY 1
 
+/* Define to 1 if you have the `std::shared_mutex' function. */
+#cmakedefine HAVE_SHARED_MUTEX 1
+
 /* Define to 1 if you have the `uselocale' function. */
 #cmakedefine HAVE_USELOCALE 1
 

cmake/helpers/configure.cmake

@@ -358 +358 @@
     set(DONT_DEPRECATE_SPRINTF 1)
     add_definitions(-DDONT_DEPRECATE_SPRINTF)
   endif ()
+  
+  check_cxx_source_compiles(
+    "
+    #include <mutex>
+    #include <shared_mutex>
+    int main(int argc, const char * argv[]) {
+        std::shared_mutex smtx;
+        int product = 0;
+        auto writer = [&smtx, &product](int start, int end)
+        {
+            for (int i = start; i < end; ++i)
+            {
+                auto data = i;
+                {
+                    std::unique_lock<std::shared_mutex> lock(smtx);
+                    product = data;
+                }
+            }
+            smtx.lock();
+            smtx.unlock();
+        };
+        auto reader = [&smtx, &product]()
+        {
+            int data = 0;
+            std::vector<int> seen;
+            do
+            {
+                {
+                    smtx.lock_shared();
+                    data = product;
+                    smtx.unlock_shared();
+                }
+            }
+            while (1);
+        };
+        return 0;
+    }
+    "
+    HAVE_SHARED_MUTEX
+  )
 
   check_include_file("linux/userfaultfd.h" HAVE_USERFAULTFD_H)
 endif ()

port/cpl_vsi_mem.cpp

@@ -50 +50 @@
 
 #include <mutex>
 // c++17 or VS2017
-#if __cplusplus >= 201703L || _MSC_VER >= 1910
+#if defined(HAVE_SHARED_MUTEX) || _MSC_VER >= 1910
 #include <shared_mutex>
 #define CPL_SHARED_MUTEX_TYPE std::shared_mutex
 #define CPL_SHARED_LOCK std::shared_lock<std::shared_mutex>