CommonPP

commonpp is a multi purpose library easing very few operations like:

• Getting metrics out of your program (counter, gauge, statistical description of sample);
• Naming your threads (and have the custom name appearing in htop, top, gdb);
• Have a really simple thread pool on top of boost::asio;
• Quick setup of boost::log;
• …

License

I chose the BSD 2-clause license, so the library can be used in any project, however I'd appreciate any bug fix, pull request and comment.

Dependencies

commonpp depends on Boost and TBB, a C++11 compiler and CMake to be built. It builds on Mac OS X and Linux. It probably build on *BSD but I did not test (yet).

Building

$> make cmake
$> make
$> make test

Why?

Although Boost and TBB are very complete low-level libraries, there are still basic features missing, the biggest being getting out metrics out of your code. commonpp will never replace Boost or TBB but instead adds some features that integrate well.

Libraries

Core

The core part is mostly utility functions or class.

• ExecuteOnScopeExit: executes a callable on scope exit. It can be canceled;
• LoggingInterface: It is a header containing several logging function on top of boost::log. Every record produced with commonpp is tagged so that it can be used in a project already using boost::log (therefore init_logging should not be called).
• RandomValuePicker: select a random value in a read only container;
• FloatingArithmeticTools: Knuth's double comparison functions;
• Options: an utility class working along with an enum to offer a simple interface to manage options, see the test;
• There are several string functions to stringify, encode, join, or get a formatted date.

Thread

The thread library is quite small:

• Thread.hpp contains a function to get/set the current thread name;

• ThreadPool is a class managing several threads calling the boost::asio::io_service::run member function:

  * It can schedule a callable to be called periodically;
  * It supports several `io_service`;
  * A function can be called on thread startup to setup any thread specific
    data;
  

• Spinlock: should be obvious

• ThreadTimer: it allows one to get the load of the current thread. This is experimental;

Metrics

This is the main reason this commonpp exists. I often found myself struggling to get metrics out of my code to monitor performances, behavior, resource usage, etc. Most of the library counters are based on the RRD ones, the ExponentiallyDecayingReservoir is based on the implementation in Codahale as well as the test.

• Metrics.hpp is the entry point of the metric library; one should use it to register counters;
• MetricTag: This represents the metadata associated with a counter; for instance if you use Graphite, the tag will be converted in a path (concatenation of all the value separated by a point), if you use InfluxDB, it will be converted in a list of tag;
• MetricValue: This holds the actual value(s) of a counter.

The counters

There are 3 types of counter:

• Counter or SharedCounter should be used to represent a value that always increases and never goes back like a request counter. The actual value sent is the rate at which the counter increases. The SharedCounter can be shared among several thread safely.
• Gauge: It represents an absolute value like a number of active connections.
• DescStat: Associated with a reservoir, it will describe the distribution of the values, for instance, one can use a reservoir to push the time a function X takes to run, and the StatDesc will give several information like the min, max, variance, quantile, mean, etc.

There is also a helper:

• TimeScope is an helper to measure the time we spent in the current scope.

Examples

There is a complete example how to use the metric library here

The reservoirs

Currently only one is implemented: ExponentiallyDecayingReservoir. Documentation can be found there.

The sinks

• Graphite: It sends a list of MetricTag and MetricValue pair in a format understood by Graphite (actually Carbon). As stated before, the values are concatenated to form the metric path, therefore the order used to insert the tag is important.
• InfluxDB: It sends the measure name along with all the tags and the value as described in the documentation. The MetricTag and MetricValue class were designed with InfluxDB primarely in mind.

Net

This library for now consist in a HTTP request generator and parser and URL encode and decode functions.

Next step

• Migrate my other project HTTPP to use commonpp;
• Add tests.