Merge pull request #5220 from adityamandaleeka/force_gc_concurrent

Check CLRConfig value explicitly to determine whether concurrent GC was forced

2 files changed, 17 insertions, 25 deletions

diff --git a/src/coreclr/hosts/unixcoreruncommon/coreruncommon.cpp b/src/coreclr/hosts/unixcoreruncommon/coreruncommon.cpp
index fb70c69ec0..1acaf4c540 100644
--- a/src/coreclr/hosts/unixcoreruncommon/coreruncommon.cpp
+++ b/src/coreclr/hosts/unixcoreruncommon/coreruncommon.cpp
@@ -28,10 +28,6 @@
 // disabled. Server GC is off by default.
 static const char* serverGcVar = "CORECLR_SERVER_GC";
 
-// Name of the environment variable controlling concurrent GC,
-// used in the same way as serverGcVar. Concurrent GC is on by default.
-static const char* concurrentGcVar = "CORECLR_CONCURRENT_GC";
-
 #if defined(__linux__)
 #define symlinkEntrypointExecutable "/proc/self/exe"
 #elif !defined(__APPLE__)
@@ -327,25 +323,16 @@ int ExecuteManagedAssembly(
         }
         else
         {
-            // check if we are enabling server GC or concurrent GC.
-            // Server GC is off by default, while concurrent GC is on by default.
-            // Actual checking of these string values is done in coreclr_initialize.
+            // Check whether we are enabling server GC (off by default)
             const char* useServerGc = std::getenv(serverGcVar);
             if (useServerGc == nullptr)
             {
                 useServerGc = "0";
             }
-            
-            const char* useConcurrentGc = std::getenv(concurrentGcVar);
-            if (useConcurrentGc == nullptr)
-            {
-                useConcurrentGc = "1";
-            }
 
             // CoreCLR expects strings "true" and "false" instead of "1" and "0".
             useServerGc = std::strcmp(useServerGc, "1") == 0 ? "true" : "false";
-            useConcurrentGc = std::strcmp(useConcurrentGc, "1") == 0 ? "true" : "false";
-            
+
             // Allowed property names:
             // APPBASE
             // - The base path of the application from which the exe and other assemblies will be loaded
@@ -369,7 +356,6 @@ int ExecuteManagedAssembly(
                 "NATIVE_DLL_SEARCH_DIRECTORIES",
                 "AppDomainCompatSwitch",
                 "System.GC.Server",
-                "System.GC.Concurrent"
             };
             const char *propertyValues[] = {
                 // TRUSTED_PLATFORM_ASSEMBLIES
@@ -384,8 +370,6 @@ int ExecuteManagedAssembly(
                 "UseLatestBehaviorWhenTFMNotSpecified",
                 // System.GC.Server
                 useServerGc,
-                // System.GC.Concurrent
-                useConcurrentGc
             };
 
             void* hostHandle;
diff --git a/src/vm/eeconfig.cpp b/src/vm/eeconfig.cpp
index ddf2048f33..27535075ea 100644
--- a/src/vm/eeconfig.cpp
+++ b/src/vm/eeconfig.cpp
@@ -794,15 +794,23 @@ HRESULT EEConfig::sync()
 
     bool gcConcurrentWasForced = false;
 #ifdef FEATURE_CORECLR
-    gcConcurrentWasForced = Configuration::GetKnobBooleanValue(W("System.GC.Concurrent"), CLRConfig::UNSUPPORTED_gcConcurrent);
-    if (gcConcurrentWasForced)
-        iGCconcurrent = TRUE;
-#else
-    int gcConcurrentConfigVal = CLRConfig::GetConfigValue(CLRConfig::UNSUPPORTED_gcConcurrent);
-    gcConcurrentWasForced = (gcConcurrentConfigVal > 0);
+    // The CLRConfig value for UNSUPPORTED_gcConcurrent defaults to -1, and treats any
+    // positive value as 'forcing' concurrent GC to be on. Because the standard logic
+    // for mapping a DWORD CLRConfig to a boolean configuration treats -1 as true (just
+    // like any other nonzero value), we will explicitly check the DWORD later if this
+    // check returns false.
+    gcConcurrentWasForced = Configuration::GetKnobBooleanValue(W("System.GC.Concurrent"), false);
+#endif
+
+    int gcConcurrentConfigVal = 0;
+    if (!gcConcurrentWasForced)
+    {
+        gcConcurrentConfigVal = CLRConfig::GetConfigValue(CLRConfig::UNSUPPORTED_gcConcurrent);
+        gcConcurrentWasForced = (gcConcurrentConfigVal > 0);
+    }
+
     if (gcConcurrentWasForced || (gcConcurrentConfigVal == -1 && g_IGCconcurrent))
         iGCconcurrent = TRUE;
-#endif
 
     // Disable concurrent GC during ngen for the rare case a GC gets triggered, causing problems
     if (IsCompilationProcess())