GC cleanup can now be configured as a DRT GC option

Author: rainers

changelog/gc_cleanup.dd

@@ -0,0 +1,26 @@
+GC cleanup can now be configured as a DRT GC option
+
+The default cleanup method for the GC is to unconditionally run a
+collection before runtime termination to finalize objects
+that are still alive and hold resources that affect system state outside
+the current process. This combines the worst of possible alternatives:
+it can cause a considerable delay and does not guarantee finalization
+of all objects as roots might still exist.
+
+The cleanup behaviour can now be configured by a DRT option to the
+$(LINK2 $(ROOT_DIR)spec/garbage.html, GC configuration),
+e.g. by passing `--DRT-gcopt=cleanup:none` on the command
+line. Three options are provided:
+
+$(UL
+  $(LI collect: run a collection (the default for backward compatibility))
+  $(LI none: do nothing)
+  $(LI finalize: all live objects are finalized unconditionally)
+)
+
+As usual, you can also embed the configuration into the application by
+redefining `rt_options`, e.g.
+
+-------
+extern(C) __gshared string[] rt_options = [ "gcopt=cleanup:none" ];
+-------

src/gc/config.d

@@ -23,6 +23,7 @@ struct Config
     size_t maxPoolSize = 64; // maximum pool size (MB)
     size_t incPoolSize = 3;  // pool size increment (MB)
     float heapSizeFactor = 2.0; // heap size to used memory ratio
+    string cleanup = "collect"; // select gc cleanup method none|collect|finalize
 
 @nogc nothrow:
 
@@ -43,6 +44,7 @@ struct Config
     maxPoolSize:N  - maximum pool size in MB (%lld)
     incPoolSize:N  - pool size increment MB (%lld)
     heapSizeFactor:N - targeted heap size to used memory ratio (%g)
+    cleanup:none|collect|finalize - how to treat live objects when terminating (collect)
 ";
         printf(s.ptr, disable, profile, cast(long)initReserve, cast(long)minPoolSize,
                cast(long)maxPoolSize, cast(long)incPoolSize, heapSizeFactor);

src/gc/proxy.d

@@ -79,20 +79,35 @@ extern (C)
 
     void gc_term()
     {
-        // NOTE: There may be daemons threads still running when this routine is
-        //       called.  If so, cleaning memory out from under then is a good
-        //       way to make them crash horribly.  This probably doesn't matter
-        //       much since the app is supposed to be shutting down anyway, but
-        //       I'm disabling cleanup for now until I can think about it some
-        //       more.
-        //
-        // NOTE: Due to popular demand, this has been re-enabled.  It still has
-        //       the problems mentioned above though, so I guess we'll see.
-
         if (isInstanceInit)
         {
-            instance.collectNoStack();  // not really a 'collect all' -- still scans
-                                        // static data area, roots, and ranges.
+            switch (config.cleanup)
+            {
+                default:
+                    import core.stdc.stdio : fprintf, stderr;
+                    fprintf(stderr, "Unknown GC cleanup method, please recheck ('%.*s').\n",
+                            cast(int)config.cleanup.length, config.cleanup.ptr);
+                    break;
+                case "none":
+                    break;
+                case "collect":
+                    // NOTE: There may be daemons threads still running when this routine is
+                    //       called.  If so, cleaning memory out from under then is a good
+                    //       way to make them crash horribly.  This probably doesn't matter
+                    //       much since the app is supposed to be shutting down anyway, but
+                    //       I'm disabling cleanup for now until I can think about it some
+                    //       more.
+                    //
+                    // NOTE: Due to popular demand, this has been re-enabled.  It still has
+                    //       the problems mentioned above though, so I guess we'll see.
+
+                    instance.collectNoStack();  // not really a 'collect all' -- still scans
+                                                // static data area, roots, and ranges.
+                    break;
+                case "finalize":
+                    instance.runFinalizers((cast(ubyte*)null)[0 .. size_t.max]);
+                    break;
+            }
 
             ManualGC.finalize(instance);
             ConservativeGC.finalize(instance);