Support setting the MMTk plan as a flag

gc.c

@@ -42,6 +42,7 @@
 #error MMTk does not use transient heap.
 #endif // USE_TRANSIENT_HEAP
 #include "mmtk.h"
+#include "internal/cmdlineopt.h"
 
 RubyUpcalls ruby_upcalls;
 #endif
@@ -156,6 +157,13 @@ RubyUpcalls ruby_upcalls;
 #define MAP_ANONYMOUS MAP_ANON
 #endif
 
+#ifdef USE_THIRD_PARTY_HEAP
+static char *mmtk_env_plan = NULL;
+static char *mmtk_pre_arg_plan = NULL;
+static char *mmtk_post_arg_plan = NULL;
+static char *mmtk_chosen_plan = NULL;
+#endif
+
 static inline struct rbimpl_size_mul_overflow_tag
 size_add_overflow(size_t x, size_t y)
 {
@@ -1442,7 +1450,7 @@ asan_poison_object_restore(VALUE obj, void *ptr)
 #define FL_SET2(x,f)   FL_CHECK2("FL_SET2",   x, RBASIC(x)->flags |= (f))
 #define FL_UNSET2(x,f) FL_CHECK2("FL_UNSET2", x, RBASIC(x)->flags &= ~(f))
 
-// Comment for easy location 
+// Comment for easy location
 #ifdef USE_THIRD_PARTY_HEAP
 #define RVALUE_MARK_BITMAP(obj)           0
 #define RVALUE_PIN_BITMAP(obj)            0
@@ -1863,10 +1871,20 @@ rb_objspace_alloc(void)
     dont_gc_on();
 
 #ifdef USE_THIRD_PARTY_HEAP
+    if (!mmtk_env_plan && setenv("MMTK_PLAN", mmtk_chosen_plan, 0) != 0) {
+        fputs("[FATAL] could not set MMTK_PLAN\n", stderr);
+	    exit(EXIT_FAILURE);
+    }
+
     // Note: the limit is currently broken for NoGC, but we still attempt to
     // initialise it properly regardless.
     // See https://github.com/mmtk/mmtk-core/issues/214
     mmtk_init_binding(rb_mmtk_heap_limit(), &ruby_upcalls);
+
+    if (!mmtk_env_plan && unsetenv("MMTK_PLAN") != 0) {
+        fputs("[FATAL] could not unset MMTK_PLAN\n", stderr);
+	    exit(EXIT_FAILURE);
+    }
 #endif
 
     return objspace;
@@ -15092,4 +15110,79 @@ size_t rb_mmtk_heap_limit(void) {
     }
 }
 
+void rb_mmtk_pre_process_opts(int argc, char **argv) {
+    mmtk_env_plan = getenv("MMTK_PLAN");
+
+    for (int n = 1; n < argc; n++) {
+        if (strcmp(argv[n], "--") == 0) {
+            break;
+        }
+        else if (strncmp(argv[n], "--mmtk-plan=", strlen("--mmtk-plan=")) == 0) {
+            mmtk_pre_arg_plan = argv[n] + strlen("--mmtk-plan=");
+        }
+    }
+
+    char *env_args = getenv("RUBYOPT");
+    if (env_args != NULL) {
+        while (*env_args != '\0') {
+            while (ISSPACE(*env_args)) {
+                env_args++;
+            }
+
+            if (strncmp(env_args, "--mmtk-plan=", strlen("--mmtk-plan=")) == 0) {
+                int length = 0;
+                while (env_args[length] != '\0' && !ISSPACE(env_args[length])) {
+                    length++;
+                }
+
+                mmtk_pre_arg_plan = strndup(env_args + strlen("--mmtk-plan="), length - strlen("--mmtk-plan="));
+                if (mmtk_pre_arg_plan == NULL) {
+                    rb_bug("could not allocate space for argument");
+                }
+                env_args += length;
+            }
+        }
+    }
+
+    if (mmtk_env_plan && mmtk_pre_arg_plan && strcmp(mmtk_env_plan, mmtk_pre_arg_plan) != 0) {
+        fputs("[FATAL] MMTK_PLAN and --mmtk-plan do not agree\n", stderr);
+	    exit(EXIT_FAILURE);
+    }
+
+    if (mmtk_env_plan) {
+        mmtk_chosen_plan = mmtk_env_plan;
+    }
+    else if (mmtk_pre_arg_plan) {
+        mmtk_chosen_plan = mmtk_pre_arg_plan;
+    }
+    else {
+        mmtk_chosen_plan = MMTK_DEFAULT_PLAN;
+    }
+}
+
+#define opt_match_noarg(s, l, name) \
+    opt_match(s, l, name) && (*(s) ? (rb_warn("argument to --mmtk-" name " is ignored"), 1) : 1)
+#define opt_match_arg(s, l, name) \
+    opt_match(s, l, name) && (*(s) ? 1 : (rb_raise(rb_eRuntimeError, "--mmtk-" name " needs an argument"), 0))
+
+void rb_mmtk_post_process_opts(char *s) {
+    const size_t l = strlen(s);
+    if (l == 0) {
+        return;
+    }
+    if (opt_match_arg(s, l, "plan")) {
+        mmtk_post_arg_plan = s + 1;
+    }
+    else {
+        rb_raise(rb_eRuntimeError,
+                 "invalid MMTk option `%s' (--help will show valid MMTk options)", s);
+    }
+}
+
+void rb_mmtk_post_process_opts_finish(void) {
+    if (strcmp(mmtk_pre_arg_plan ? mmtk_pre_arg_plan : "", mmtk_post_arg_plan ? mmtk_post_arg_plan : "") != 0) {
+        rb_raise(rb_eRuntimeError, "--mmtk-plan values disagree");
+    }
+}
+
 #endif

main.c

@@ -30,10 +30,17 @@
 # undef RUBY_DEBUG_ENV
 #endif
 
+#ifdef USE_THIRD_PARTY_HEAP
+#include "mmtk.h"
+#endif
+
 static int
 rb_main(int argc, char **argv)
 {
     RUBY_INIT_STACK;
+#ifdef USE_THIRD_PARTY_HEAP
+    rb_mmtk_pre_process_opts(argc, argv);
+#endif
     ruby_init();
     return ruby_run_node(ruby_options(argc, argv));
 }

mmtk.h

@@ -22,6 +22,8 @@ typedef void* MMTk_VMMutatorThread;
 #define MMTK_GC_THREAD_KIND_CONTROLLER 0
 #define MMTK_GC_THREAD_KIND_WORKER 1
 
+#define MMTK_DEFAULT_PLAN "MarkSweep"
+
 typedef struct {
     void (*init_gc_worker_thread)(MMTk_VMWorkerThread worker_tls);
     MMTk_VMWorkerThread (*get_gc_thread_tls)(void);
@@ -104,6 +106,10 @@ extern void mmtk_harness_end(void *tls);
 extern void mmtk_register_finalizable(void *reff);
 extern void* mmtk_poll_finalizable(bool include_live);
 
+void rb_mmtk_pre_process_opts(int argc, char **argv);
+void rb_mmtk_post_process_opts(char *arg);
+void rb_mmtk_post_process_opts_finish(void);
+
 #ifdef __cplusplus
 }
 #endif

ruby.c

@@ -61,6 +61,10 @@
 #include "ruby/version.h"
 #include "ruby/internal/error.h"
 
+#ifdef USE_THIRD_PARTY_HEAP
+#include "mmtk.h"
+#endif
+
 #ifndef MAXPATHLEN
 # define MAXPATHLEN 1024
 #endif
@@ -333,6 +337,11 @@ usage(const char *name, int help, int highlight, int columns)
         M("--yjit-max-versions=num",   "", "Maximum number of versions per basic block (default: 4)"),
         M("--yjit-greedy-versioning",  "", "Greedy versioning mode (default: disabled)"),
     };
+#endif
+#ifdef USE_THIRD_PARTY_HEAP
+    static const struct ruby_opt_message mmtk_options[] = {
+        M("--mmtk-plan=name",          "", "MMTk garbage collection plan to use (default: " MMTK_DEFAULT_PLAN ")"),
+    };
 #endif
     int i;
     const char *sb = highlight ? esc_standout+1 : esc_none;
@@ -370,6 +379,11 @@ usage(const char *name, int help, int highlight, int columns)
     for (i = 0; i < numberof(yjit_options); ++i)
         SHOW(yjit_options[i]);
 #endif
+#ifdef USE_THIRD_PARTY_HEAP
+    printf("%s""MMTk options (experimental):%s\n", sb, se);
+    for (i = 0; i < numberof(mmtk_options); ++i)
+        SHOW(mmtk_options[i]);
+#endif
 }
 
 #define rubylib_path_new rb_str_new
@@ -1439,6 +1453,15 @@ proc_options(long argc, char **argv, ruby_cmdline_options_t *opt, int envopt)
                 setup_yjit_options(s);
 #else
                 rb_warn("Ruby was built without YJIT support");
+#endif
+            }
+            else if (is_option_with_optarg("mmtk", '-', true, false, false)) {
+#ifdef USE_THIRD_PARTY_HEAP
+                rb_mmtk_post_process_opts(s);
+#undef opt_match_noarg
+#undef opt_match_arg
+#else
+                rb_warn("Ruby was built without MMTk support");
 #endif
             }
 	    else if (strcmp("yydebug", s) == 0) {
@@ -1805,6 +1828,10 @@ process_options(int argc, char **argv, ruby_cmdline_options_t *opt)
         FEATURE_SET_RESTORE(opt->warn, warn);
     }
 
+#ifdef USE_THIRD_PARTY_HEAP
+    rb_mmtk_post_process_opts_finish();
+#endif
+
     if (opt->src.enc.name)
         /* cannot set deprecated category, as enabling deprecation warnings based on flags
          * has not happened yet.

test/lib/jit_support.rb

@@ -56,7 +56,7 @@ def eval_with_jit_without_retry(env = nil, script, verbose: 0, min_calls: 5, sav
   end
 
   def supported?
-    return false if RbConfig::CONFIG["CFLAGS"].include?("USE_THIRD_PARTY_HEAP")
+    return false if defined?(GC::MMTk)
     return @supported if defined?(@supported)
     @supported = RbConfig::CONFIG["MJIT_SUPPORT"] != 'no' && UNSUPPORTED_COMPILERS.all? do |regexp|
       !regexp.match?(RbConfig::CONFIG['MJIT_CC'])

version.c

@@ -16,6 +16,10 @@
 #include "yjit.h"
 #include <stdio.h>
 
+#ifdef USE_THIRD_PARTY_HEAP
+#include "mmtk.h"
+#endif
+
 #ifndef EXIT_SUCCESS
 #define EXIT_SUCCESS 0
 #endif
@@ -48,7 +52,7 @@ const char ruby_copyright[] = RUBY_COPYRIGHT;
 const char ruby_engine[] = "ruby";
 
 // Enough space for any combination of option flags
-static char ruby_dynamic_description_buffer[sizeof(ruby_description) + sizeof("+MJIT +YJIT +MMTk") - 1];
+static char ruby_dynamic_description_buffer[sizeof(ruby_description) + sizeof("+MJIT +YJIT +MMTk(XXXXXXXXXXXXXXXX)") - 1];
 
 // Might change after initialization
 const char *rb_dynamic_description = ruby_description;
@@ -107,14 +111,16 @@ Init_version(void)
 void
 Init_ruby_description(void)
 {
-    if (snprintf(ruby_dynamic_description_buffer, sizeof(ruby_dynamic_description_buffer), "%s%s%s%s%s",
+    if (snprintf(ruby_dynamic_description_buffer, sizeof(ruby_dynamic_description_buffer), "%s%s%s%s%s%s%s",
             ruby_description_pre,
             MJIT_OPTS_ON ? " +MJIT" : "",
             rb_yjit_enabled_p() ? " +YJIT" : "",
 #ifdef USE_THIRD_PARTY_HEAP
-            " +MMTk",
+            " +MMTk(",
+            mmtk_plan_name(),
+            ")",
 #else
-            "",
+            "", "", "",
 #endif
             ruby_description_post) < 0) {
         rb_bug("could not format dynamic description string");

vm_dump.c

@@ -1196,6 +1196,7 @@ rb_vm_bugreport(const void *ctx)
 
 #ifdef USE_THIRD_PARTY_HEAP
     fprintf(stderr, "* MMTk:\n\n");
+    fprintf(stderr, "                mmtk_plan_name: %s\n", mmtk_plan_name());
     fprintf(stderr, "               mmtk_free_bytes: %zu\n", mmtk_free_bytes());
     fprintf(stderr, "              mmtk_total_bytes: %zu\n", mmtk_total_bytes());
     fprintf(stderr, "               mmtk_used_bytes: %zu\n", mmtk_used_bytes());