[mono] Set thread suspend default in mono.proj; default to hybrid (#4…

…6873)

* [mono] Set thread suspend default in mono.proj; default to hybrid

Instead of detecting in cmake, make a decision in mono.proj

* [cmake] Pick a fallback suspend policy if GC_SUSPEND is default

* cleanup mono.proj

* default to "preemptive" on wasm

It isn't really preemptive, it just turns off safepoint code in the AOT
compiler.  This is fine for single threaded.

src/mono/CMakeLists.txt

@@ -216,7 +216,6 @@ elseif(CMAKE_SYSTEM_NAME STREQUAL "Android")
   set(ANDROID_UNIFIED_HEADERS 1)
   set(ENABLE_MONODROID 1)
   set(DISABLE_EXECUTABLES 1)
-  set(GC_SUSPEND "hybrid")
   # Force some defines
   set(HAVE_SCHED_GETAFFINITY 0)
   set(HAVE_SCHED_SETAFFINITY 0)
@@ -264,9 +263,6 @@ if(TARGET_SYSTEM_NAME STREQUAL "Darwin")
   set(TARGET_MACH 1)
   set(TARGET_OSX 1)
   set(TARGET_DARWIN 1)
-  if (GC_SUSPEND STREQUAL "default")
-    set(GC_SUSPEND "hybrid")
-  endif()
 elseif(TARGET_SYSTEM_NAME STREQUAL "iOS" OR TARGET_SYSTEM_NAME STREQUAL "tvOS")
   set(TARGET_MACH 1)
   set(TARGET_IOS 1)
@@ -552,6 +548,20 @@ if (GC_SUSPEND STREQUAL "coop")
   set(ENABLE_COOP_SUSPEND 1)
 elseif(GC_SUSPEND STREQUAL "hybrid")
   set(ENABLE_HYBRID_SUSPEND 1)
+elseif(GC_SUSPEND STREQUAL "preemptive")
+elseif(GC_SUSPEND STREQUAL "default")
+  # set some kind of fallback default
+  if(TARGET_SYSTEM_NAME STREQUAL "watchOS")
+    set(ENABLE_COOP_SUSPEND 1)
+  elseif(TARGET_SYSTEM_NAME STREQUAL "Windows")
+    # use preemptive
+  elseif(TARGET_SYSTEM_NAME STREQUAL "Emscripten")
+    # use preemptive
+  else()
+    set(ENABLE_HYBRID_SUSPEND 1)
+  endif()
+else()
+  message(FATAL_ERROR "GC_SUSPEND (set to '${GC_SUSPEND}') must be one of coop, hybrid or preemptive")
 endif()
 
 ######################################

src/mono/mono.proj

@@ -9,6 +9,7 @@
       - MonoAOTLLVMDir - [optional] the directory where LLVM is located, for an AOT-only Mono
       - MonoVerboseBuild - enable verbose build
       - MonoMetadataUpdate - enable experimental method body replacement code
+      - MonoThreadSuspend - coop,hybrid,preemptive - default thread suspend mode
   -->
 
   <PropertyGroup>
@@ -49,6 +50,15 @@
     <MonoCxxCompiler Condition="'$(MonoCCompiler)' == 'gcc'">g++</MonoCxxCompiler>
   </PropertyGroup>
 
+  <!-- default thread suspend for specific platforms -->
+  <PropertyGroup>
+    <MonoThreadSuspend Condition="'$(TargetswatchOS)' == 'true' and '$(MonoThreadSuspend)' == ''">coop</MonoThreadSuspend>
+    <!-- wasm isn't really preemptive, but we don't want safepoints -->
+    <MonoThreadSuspend Condition="'$(TargetsBrowser)' == 'true' and '$(MonoThreadSuspend)' == ''">preemptive</MonoThreadSuspend>
+    <!-- all other platforms -->
+    <MonoThreadSuspend Condition="'$(MonoThreadSuspend)' == ''">hybrid</MonoThreadSuspend>
+  </PropertyGroup>
+
   <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
     <PackageReference Include="Microsoft.NETCore.Runtime.ICU.Transport" PrivateAssets="all" Version="$(MicrosoftNETCoreRuntimeICUTransportVersion)" GeneratePathProperty="true" />
   </ItemGroup>
@@ -126,6 +136,7 @@
       <_MonoCMakeArgs Include="-DCMAKE_INSTALL_LIBDIR=lib"/>
       <_MonoCMakeArgs Include="-DCMAKE_BUILD_TYPE=$(Configuration)"/>
       <_MonoCMakeArgs Condition="'$(MonoEnableLLVM)' == 'true'" Include="-DLLVM_PREFIX=$(MonoLLVMDir)" />
+      <_MonoCMakeArgs Include="-DGC_SUSPEND=$(MonoThreadSuspend)" />
     </ItemGroup>
 
     <!-- We build LLVM bits for x64 Linux without C++11 ABI (CentOS 7 has libstdc++ < 5.1) -->
@@ -434,7 +445,10 @@
       <!-- FIXME: Add sanity check that the interpreter is enabled -->
       <MonoAOTCMakeArgs Condition="'$(MonoMetadataUpdate)' == 'true'" Include="-DENABLE_METADATA_UPDATE=1" />
 
-      <!-- Select generator platform for VS generator -->
+      <!-- thread suspend -->
+      <MonoAOTCMakeArgs Include="-DGC_SUSPEND=$(MonoThreadSuspend)" />
+
+     <!-- Select generator platform for VS generator -->
       <MonoAOTCMakeArgs Condition="'$(OS)' == 'Windows_NT' and '$(_MonoUseNinja)' != 'true' and '$(Platform)' == 'x64'" Include="-A x64" />
       <MonoAOTCMakeArgs Condition="'$(OS)' == 'Windows_NT' and '$(_MonoUseNinja)' != 'true' and '$(Platform)' == 'x86'" Include="-A Win32" />
       <MonoAOTCMakeArgs Condition="'$(OS)' == 'Windows_NT' and '$(_MonoUseNinja)' != 'true' and '$(Platform)' == 'arm'" Include="-A ARM" />