Prevent attempted re-enabling of providers breaking existing probes.

It was possible to call enable() on a provider more than once, which would
simply attempt to repeat the work required - creating stubs and the appropriate DOF.
However the kernel will in most cases ignore new DOF, leaving the old provider
in place, while the newly-created stubs are elsewhere.

This change simply no-ops subsequent calls to enable() on a provider, which still
doesn't allow changes to be made, but does prevent inadvertent breaking of existing
probes.

dtrace_provider.cc

@@ -90,6 +90,10 @@ namespace node {
       return Undefined();
     }
 
+    if (provider->enabled == 1) {
+      return Undefined();
+    }
+
     DOFSection *probes = new DOFSection(DOF_SECT_PROBES, 1);
 
     // PROBES SECTION
@@ -198,6 +202,7 @@ namespace node {
 
     provider->file = file;
 
+    provider->enabled = 1;
     return Undefined();
   }
 

dtrace_provider.h

@@ -193,6 +193,7 @@ namespace node {
   public:
     static void Initialize(v8::Handle<v8::Object> target);
     char *name;
+    int enabled;
     DTraceProbeDef *probe_defs;
     DTraceProbe *probes;
     DOFFile *file;
@@ -207,6 +208,7 @@ namespace node {
       probe_defs = NULL;
       probes = NULL;
       file = NULL;
+      enabled = 0;
     }
 
     ~DTraceProvider() {

test/dtp.js

@@ -1,8 +1,21 @@
+// expected output:
+//
+// $ sudo dtrace -Z -n 'nodeapp*:::probe1{ printf("%i %i %i %i %i %i", arg0, arg1, arg2, arg3, arg4, arg5); }' \
+//                  -n 'nodeapp*:::probe2{ printf("%s %s %s %s %s %s", copyinstr(arg0), copyinstr(arg1), copyinstr(arg2), copyinstr(arg3), copyinstr(arg4), copyinstr(arg5)) }' \
+//                  -c 'node test/dtp.js'
+//
+// dtrace: description 'nodeapp*:::probe1' matched 0 probes
+// dtrace: description 'nodeapp*:::probe2' matched 0 probes
+// CPU     ID                    FUNCTION:NAME
+//  1   3421                      func:probe1 1 2 3 4 5 6
+//  1   3422                      func:probe2 a b c d e f
+
 var d = require('../dtrace-provider');
 var dtp = d.createDTraceProvider("nodeapp");
 dtp.addProbe("probe1", "int", "int", "int", "int", "int", "int");
 dtp.addProbe("probe2", "char *", "char *", "char *", "char *", "char *", "char *");
 dtp.enable();
 dtp.fire("probe1", function(p) { return [1, 2, 3, 4, 5, 6]; });
-dtp.fire("probe2", function(p) { return ["hello, dtrace", "foo", "bar", "baz", "fred", "barney"]; });
+dtp.fire("probe2", function(p) { return ["a", "b", "c", "d", "e", "f"]; });
 
+setTimeout(function() { }, 1000);

test/enabled_again.js

@@ -0,0 +1,19 @@
+// expected output:
+// 
+// $ sudo dtrace -Zn 'nodeapp*:::{ trace(arg0); }' -c 'node test/enabled_again.js'
+// dtrace: description 'nodeapp*:::' matched 0 probes
+// CPU     ID                    FUNCTION:NAME
+//   1   5456                      func:probe1                 1
+//   1   5456                      func:probe1                 2
+
+var d = require('../dtrace-provider');
+var dtp = d.createDTraceProvider("nodeapp");
+dtp.addProbe("probe1", "int");
+dtp.enable();
+dtp.fire("probe1", function(p) { return [1]; });
+
+for (var i = 0; i<100; i++) {
+    dtp.enable();
+}
+dtp.fire("probe1", function(p) { return [2]; });
+setTimeout(function() { }, 1000);