This extension allows you to create native DTrace providers for your Node.js applications. That is, to create providers and probes which expose information specific to your application, rather than information about the node runtime.

You could use this to expose high-level information about the inner workings of your application, or to create a specific context in which to look at information from other runtime or system-level providers.

The provider is not created in the usual way, by declaring it, and then changing the build process to include it, but dynamically at runtime. This is done entirely in-process, and there is no background compiler invocation. The process creating the provider need not run as root.

EXAMPLE

Here's a simple example of creating a provider:

var d = require('dtrace-provider');

var dtp = d.createDTraceProvider("nodeapp"); dtp.addProbe("probe1", "int", "int"); dtp.addProbe("probe2", "char *"); dtp.enable(); dtp.fire("probe1", function(p) { return [1, 2]; }); dtp.fire("probe2", function(p) { return ["hello, dtrace"]; });

This example creates a provider called "nodeapp", and adds two probes. It then enables the provider, at which point the provider becomes visible to DTrace.

The probes are then fired, which produces this output:

$ sudo dtrace -Z -n 'nodeapp*:::probe1{ trace(arg0); trace(arg1) }'
-n 'nodeapp*:::probe2{ trace(copyinstr(arg0)); }' dtrace: description 'nodeapp*:::probe1' matched 0 probes dtrace: description 'nodeapp*:::probe2' matched 0 probes CPU ID FUNCTION:NAME 1 123562 func:probe1 1 2 1 123563 func:probe2 hello, dtrace

PLATFORM SUPPORT

The nature of this extension means that support must be added for each platform. Right now that support is only in place for OS X, 64 bit, but Solaris x86 and 32 bit support is on the way.

LIMITATIONS

The maximum number of probe arguments is 6. There's scope to increase this, with some extra complexity in the platform-specific code.

The data types supported are "int" and "char *". There's definitely scope to improve this, with more elaborate argument handling.

CAVEATS

This is the first working version, and there are a number of important cleanups to be made. Creating a provider will leak memory, although firing a probe should not.

Performance is not where it should be, most especially the disabled-probe effect. Probes are already using the "is-enabled" feature of DTrace, but too much work needs to be done to get there. Improving this may imply changes to the API shown in the example above.