Libdatahike - C/C++ Native Library

Libdatahike provides a C/C++ interface to Datahike, allowing you to use Datahike databases from native applications. This library is built using GraalVM Native Image.

Maturity

This feature of Datahike is still early and is subject to change.

Building

To build the native library and test executable you need GraalVM-JDK installed with native-compile, babashka and Clojure.

# Compile the native library
bb ni-compile

# Compile the C++ test executable
./libdatahike/compile-cpp

This will create:

• libdatahike/target/libdatahike.so - The shared library
• libdatahike/target/test_cpp - Test executable

API Functions

The library provides the following C functions (defined in libdatahike/target/libdatahike.h):

Database Operations

• create_database(thread, config, format, callback) - Create a new database
• database_exists(thread, config, format, callback) - Check if database exists
• delete_database(thread, config, format, callback) - Delete a database

Data Operations

• transact(thread, config, input_format, data, output_format, callback) - Execute transactions
• query(thread, query, num_inputs, input_formats, inputs, output_format, callback) - Execute queries
• pull(thread, config, format, pattern, entity_id, output_format, callback) - Pull entity data
• pull_many(thread, config, format, pattern, entity_ids, output_format, callback) - Pull multiple entities
• entity(thread, config, format, entity_id, output_format, callback) - Get entity
• datoms(thread, config, format, index, components, callback) - Get datoms
• schema(thread, config, format, output_format, callback) - Get schema
• reverse_schema(thread, config, format, output_format, callback) - Get reverse schema

Utility Operations

• metrics(thread, config, format, output_format, callback) - Get database metrics
• gc_storage(thread, config, older_than, output_format, callback) - Garbage collect storage

Usage Example

C++ Example

Please take a look at the C++ example that is part of our test suite: [../libdatahike/src/test_cpp.cpp]

Data Formats

The library supports multiple data formats:

• "edn" - Extensible Data Notation (default)
• "json" - JSON format
• "cbor" - RFC 8949 Concise Binary Object Representation

Error Handling

Errors are returned through the callback functions as strings. Always check the callback results for error conditions.

Memory Management

• The GraalVM isolate should be created once and reused
• Callback functions receive string data that should be processed immediately
• The library handles memory management for internal operations

Thread Safety

Each thread requires its own graal_isolatethread_t. For multi-threaded applications, create separate thread contexts for each thread that will use the library.

Building Your Application

When building applications that use libdatahike:

# Compile your C++ code
g++ -I./libdatahike/target -L./libdatahike/target -ldatahike -o your_app your_app.cpp

# Run with library path
LD_LIBRARY_PATH=./libdatahike/target ./your_app

# or on MacOS
DYLD_LIBRARY_PATH=./libdatahike/target ./your_app