make wait_on_address configurable via cmake

CMakeLists.txt

@@ -27,6 +27,7 @@ option(SNMALLOC_LINK_ICF "Link with Identical Code Folding" ON)
 option(SNMALLOC_IPO "Link with IPO/LTO support" OFF)
 option(SNMALLOC_BENCHMARK_INDIVIDUAL_MITIGATIONS "Build tests and ld_preload for individual mitigations" OFF)
 option(SNMALLOC_ENABLE_DYNAMIC_LOADING "Build such that snmalloc can be dynamically loaded. This is not required for LD_PRELOAD, and will harm performance if enabled." OFF)
+option(SNMALLOC_ENABLE_WAIT_ON_ADDRESS "Use wait on address backoff strategy if it is available" ON)
 # Options that apply only if we're not building the header-only library
 cmake_dependent_option(SNMALLOC_RUST_SUPPORT "Build static library for rust" OFF "NOT SNMALLOC_HEADER_ONLY_LIBRARY" OFF)
 cmake_dependent_option(SNMALLOC_STATIC_LIBRARY "Build static libraries" ON "NOT SNMALLOC_HEADER_ONLY_LIBRARY" OFF)
@@ -196,6 +197,13 @@ if(SNMALLOC_USE_CXX17)
 else()
   target_compile_features(snmalloc INTERFACE cxx_std_20)
 endif()
+
+if(SNMALLOC_ENABLE_WAIT_ON_ADDRESS)
+  target_compile_definitions(snmalloc INTERFACE SNMALLOC_USE_WAIT_ON_ADDRESS=1)
+else()
+  target_compile_definitions(snmalloc INTERFACE SNMALLOC_USE_WAIT_ON_ADDRESS=0)
+endif()
+
 # https://learn.microsoft.com/en-us/cpp/build/reference/zc-cplusplus
 if(MSVC)
   target_compile_options(snmalloc INTERFACE "/Zc:__cplusplus")

src/snmalloc/ds/combininglock.h

@@ -41,8 +41,9 @@ namespace snmalloc
   class CombiningLockNode
   {
     template<typename Pal>
-    static constexpr bool has_wait_on_address =
-      pal_supports<PalFeatures::WaitOnAddress, Pal>;
+    static constexpr bool use_wait_on_address =
+      pal_supports<PalFeatures::WaitOnAddress, Pal> &&
+      SNMALLOC_USE_WAIT_ON_ADDRESS;
 
     template<bool HasWaitOnAddress, typename Pal>
     struct WaitWordTypeSelect;
@@ -60,7 +61,7 @@ namespace snmalloc
     };
 
     using WaitingWordType =
-      typename WaitWordTypeSelect<has_wait_on_address<DefaultPal>, DefaultPal>::
+      typename WaitWordTypeSelect<use_wait_on_address<DefaultPal>, DefaultPal>::
         type;
 
     template<typename F>
@@ -104,7 +105,7 @@ namespace snmalloc
     template<typename Pal = DefaultPal>
     static void wake(CombiningLockNode* node, LockStatus message)
     {
-      if constexpr (!has_wait_on_address<Pal>)
+      if constexpr (!use_wait_on_address<Pal>)
       {
         node->set_status(message);
       }
@@ -122,7 +123,7 @@ namespace snmalloc
     template<typename Pal = DefaultPal>
     void wait()
     {
-      if constexpr (!has_wait_on_address<Pal>)
+      if constexpr (!use_wait_on_address<Pal>)
       {
         while (status.load(std::memory_order_acquire) == LockStatus::WAITING)
           Aal::pause();