process.memoryUsage() fails when file descriptors are exhausted

[othiym23]

A few users of the module have encountered a condition where the memory usage sampler is failing because there are no file descriptors available. This happens with all versions of Node after 0.6.x.

Under Node 0.8.12 on Linux, process.memoryUsage() works by calling a libuv function that parses the output of /proc/self/stat. That file access is written in straight C, synchronous and coded very defensively (so many gotos…), and is tested both by benchmarking code and by burn-in tests (in Node itself).

Under Node 0.6.17, process.memoryUsage() calls a function on a Platform class defined for each supported operating system.

The sampler call in the agent acts as a sentinel of sorts – if the process has hit the maximum number of open file descriptors for the system, attempts to sample memory usage will fail. It runs once a minute, so as long as the system is starved for descriptors, it's going to trigger a new error. It's not clear to me whether it's a net win to trap the exception that gets thrown, which looks like:

Error: Too many open files
    at sampleMemory (/home/www/sites/nodechute/releases/20130220004853/node_modules/newrelic/lib/sampler.js:24:23)
    at Timer.<anonymous> (native)
    at Timer.ontimeout (timers.js:223:14)

The main reason to do so would be to prevent module users from thinking that it's the module that's causing the problem, and there's some diagnostic value in tracing that a particular error (file handle exhaustion) is happening rather than a general error (the agent can't function because the process is in a bad state).

[txase]

We haven't seen any recent reports of this issue, so I'm closing it out.