Github: https://github.com/decibelcooper/proio

• Go
  • Implemented. See docs and issues for more information
• Python
  • Implemented. See docs and issues for more information
• C++
  • Implemented. See docs and issues for more information
• Java
  • Currently read only. See docs and issues for more information

Proio is a library and set of tools that provide a simple but powerful and performant IO for physics events. Proio uses Google's protocol buffer libraries and aims simply to add the concept of an event to a protocol buffer IO. This work was inspired and influenced by LCIO, ProMC (Sergei Chekanov), and EicMC (Alexander Kiselev). Another primary goal of proio is to be language-neutral, in the sense that users can be free to use Go, Python, C++, or Java without any significant drawback to any particular choice (proio is under active developement, please see above for status). Each language implementation is written natively, and protobuf compilers generate code in each language from a single source. The protobuf messages described in the generated code are used by the proio libraries to produce serialized event structures for IO.

The proio event structures can contain any protobuf messages that the user wishes to write to the stream or file. Each event contains a list of entries which are the user data structures (required to be protobuf message implementations). This list of entries is organized with the use of tags.

A tag is a mapping from a human-readable string to a set of event entries. Each event carries a list of tags that point to unique entry IDs. The concept of tags replaces the concept of collections in LCIO. The difference between collections and tags is that a given tag can point to any type of data structure, and any number of tags may point to the same entry.

Events also carry a list of protobuf message types entered into the event by the user. These are string identifiers used by the protobuf libraries and specified by the writers of the protobuf files. Proio is distributed with common messages that are organized into data models. For example, proio.model.lcio.MCParticle is one available type that is distributed with proio. Users can create and use their own types, but most users do not need to do this, or even worry about protobuf messages at all. The libraries automatically determine the types of the entries and store them. When reading a file, the proio libraries use these type identifiers to look up message descriptors in memory, and create objects of the appropriate type in memory to then fill with the stored data.

Following the example of LCIO, the concept of persistently referencing entries from other entries to establish relationships is supported in proio. For each entry added to the event by the user, a unique ID is returned which can be stored, e.g., by another entry. This ID can later be used to retrieve the desired entry from the event object. For example, the ID of a corresponding MC particle entry can be stored in a tracker hit entry to facilitate evaluation of tracking software.

Proio writes events into what are called buckets. A bucket is a collection of sequential events that are compressed together, and has a header describing the contents of the bucket (e.g. compression type and number of events contained). The proio library adds events to a bucket until the bucket starts to overflow based on a specified target bucket size in bytes, at which point the bucket is written out to the stream or file. The proio reader can use the lightweight bucket headers to efficiently scan the contents of a file. The bucket headers are implemented as protobuf messages, so additional metadata can be added to the headers without breaking compatibility. Additionally, bucket headers can store protobuf file descriptor protos. These can be added to the stream by the writer so that the reader has all of the information needed to read the user's event data, even without having access to the particular protobuf message code used by the user.

Compression type is set per-bucket, and can be GZIP, LZ4, or uncompressed.

Bucket headers also introduce metadata to the stream in a way that is simple for the user. Metadata can be any slowly-changing information that is common to multiple events. Metadata can be added with proio writers, and is automatically associated with events when the stream is read by proio readers. Each metadata entry has a string key, can be added at any point in the stream, and is associated with all future events until a particular key is overridden at a future point in the stream.

The best way to get started with proio is to look at examples. First, pick a language of your choice, and navigate to that subdirectory in this repository. Follow the installation instructions given in the corresponding README.md, and then follow some examples that are described there as well.

Most proio tools are written in go. To fetch and build them, first make sure you have the go compiler installed on your system, and make sure your GOPATH and PATH environment variables are set up appropriately to effectively use go get. A typical configuration is to set GOPATH=$HOME and PATH=$GOPATH/bin:$PATH. Then, let's grab and install the proio package and tools:

go get github.com/decibelcooper/proio/go-proio/...

• proio-ls
• proio-summary
• proio-strip
• lcio2proio