rt: Factor out the logic that handles the various magic debug environment variables

src/rt/rust_cc.cpp

@@ -1,6 +1,7 @@
 // Rust cycle collector. Temporary, but will probably stick around for some
 // time until LLVM's GC infrastructure is more mature.
 
+#include "rust_debug.h"
 #include "rust_gc.h"
 #include "rust_internal.h"
 #include "rust_shape.h"
@@ -434,14 +435,8 @@ do_cc(rust_task *task) {
 
 void
 maybe_cc(rust_task *task) {
-    // FIXME: We ought to lock this.
-    static int zeal = -1;
-    if (zeal == -1) {
-        char *ev = getenv("RUST_CC_ZEAL");
-        zeal = ev && ev[0] != '\0' && ev[0] != '0';
-    }
-
-    if (zeal)
+    static debug::flag zeal("RUST_CC_ZEAL");
+    if (*zeal)
         do_cc(task);
 }
 

src/rt/rust_debug.h

@@ -0,0 +1,33 @@
+// Routines useful when debugging the Rust runtime.
+
+#ifndef RUST_DEBUG_H
+#define RUST_DEBUG_H
+
+#include <cstdlib>
+
+namespace debug {
+
+class flag {
+private:
+    const char *name;
+    bool valid;
+    bool value;
+
+public:
+    flag(const char *in_name) : name(in_name), valid(false) {}
+
+    bool operator*() {
+        // FIXME: We ought to lock this.
+        if (!valid) {
+            char *ev = getenv(name);
+            value = ev && ev[0] != '\0' && ev[0] != '0';
+            valid = true;
+        }
+        return value;
+    }
+};
+
+}   // end namespace debug
+
+#endif
+

src/rt/rust_gc.cpp

@@ -7,6 +7,7 @@
 #include <stdint.h>
 
 #include "rust_abi.h"
+#include "rust_debug.h"
 #include "rust_gc.h"
 #include "rust_internal.h"
 #include "rust_shape.h"
@@ -180,14 +181,9 @@ maybe_gc(rust_task *task) {
     if (*safe_point_data == NULL)
         return;
 
-    // FIXME: We ought to lock this.
-    static int zeal = -1;
-    if (zeal == -1) {
-        char *ev = getenv("RUST_GC_ZEAL");
-        zeal = ev && ev[0] != '\0' && ev[0] != '0';
-    }
+    static debug::flag zeal("RUST_GC_ZEAL");
 
-    if (zeal) {
+    if (*zeal) {
         gc gc(task);
         gc.run();
     }