Fix BLOCK_SIZE macro conflict with system headers

When including system headers like <linux/fs.h> which define BLOCK_SIZE
as a macro (usually 1024), it conflicts with the BLOCK_SIZE constant in
concurrentqueue. This causes compilation errors.

Add push/pop macro guards around the entire file to temporarily undefine
BLOCK_SIZE if it exists, and restore it after.

This is a common issue when using concurrentqueue with io_uring or other
Linux headers that define BLOCK_SIZE. The fix uses #pragma push_macro/
pop_macro which is supported by GCC, Clang, and MSVC.

Author: caomengxuan666

blockingconcurrentqueue.h

@@ -7,6 +7,13 @@
 
 #pragma once
 
+// Work around potential conflict with system headers (e.g., <linux/fs.h>) that define BLOCK_SIZE as a macro
+#ifdef BLOCK_SIZE
+#pragma push_macro("BLOCK_SIZE")
+#undef BLOCK_SIZE
+#define CONCURRENTQUEUE_BLOCK_SIZE_WAS_DEFINED
+#endif
+
 #include "concurrentqueue.h"
 #include "lightweightsemaphore.h"
 
@@ -580,3 +587,9 @@ inline void swap(BlockingConcurrentQueue<T, Traits>& a, BlockingConcurrentQueue<
 }
 
 }	// end namespace moodycamel
+
+// Restore BLOCK_SIZE macro if it was defined before
+#ifdef CONCURRENTQUEUE_BLOCK_SIZE_WAS_DEFINED
+#pragma pop_macro("BLOCK_SIZE")
+#undef CONCURRENTQUEUE_BLOCK_SIZE_WAS_DEFINED
+#endif

concurrentqueue.h

@@ -50,6 +50,13 @@
 #pragma warning(disable: 4127)  // conditional expression is constant
 #endif
 
+// Work around potential conflict with system headers (e.g., <linux/fs.h>) that define BLOCK_SIZE as a macro
+#ifdef BLOCK_SIZE
+#pragma push_macro("BLOCK_SIZE")
+#undef BLOCK_SIZE
+#define CONCURRENTQUEUE_BLOCK_SIZE_WAS_DEFINED
+#endif
+
 #if defined(__APPLE__)
 #include "TargetConditionals.h"
 #endif
@@ -3738,6 +3745,12 @@ inline void swap(typename ConcurrentQueue<T, Traits>::ImplicitProducerKVP& a, ty
 
 }
 
+// Restore BLOCK_SIZE macro if it was defined before
+#ifdef CONCURRENTQUEUE_BLOCK_SIZE_WAS_DEFINED
+#pragma pop_macro("BLOCK_SIZE")
+#undef CONCURRENTQUEUE_BLOCK_SIZE_WAS_DEFINED
+#endif
+
 #if defined(_MSC_VER) && (!defined(_HAS_CXX17) || !_HAS_CXX17)
 #pragma warning(pop)
 #endif