Cross-Language Programming#

This page will show you how to use Ray’s cross-language programming feature.

Setup the driver#

We need to set Code Search Path in your driver.

Python

import ray

ray.init(job_config=ray.job_config.JobConfig(code_search_path=["/path/to/code"]))

Java

java -classpath <classpath> \
    -Dray.address=<address> \
    -Dray.job.code-search-path=/path/to/code/ \
    <classname> <args>

You may want to include multiple directories to load both Python and Java code for workers, if they are placed in different directories.

Python

import ray

ray.init(job_config=ray.job_config.JobConfig(code_search_path="/path/to/jars:/path/to/pys"))

Java

java -classpath <classpath> \
    -Dray.address=<address> \
    -Dray.job.code-search-path=/path/to/jars:/path/to/pys \
    <classname> <args>

Python calling Java#

Suppose we have a Java static method and a Java class as follows:

package io.ray.demo;

public class Math {

  public static int add(int a, int b) {
    return a + b;
  }
}

package io.ray.demo;

// A regular Java class.
public class Counter {

  private int value = 0;

  public int increment() {
    this.value += 1;
    return this.value;
  }
}

Then, in Python, we can call the above Java remote function, or create an actor from the above Java class.

import ray

with ray.init(job_config=ray.job_config.JobConfig(code_search_path=["/path/to/code"])):
  # Define a Java class.
  counter_class = ray.cross_language.java_actor_class(
        "io.ray.demo.Counter")

  # Create a Java actor and call actor method.
  counter = counter_class.remote()
  obj_ref1 = counter.increment.remote()
  assert ray.get(obj_ref1) == 1
  obj_ref2 = counter.increment.remote()
  assert ray.get(obj_ref2) == 2

  # Define a Java function.
  add_function = ray.cross_language.java_function(
        "io.ray.demo.Math", "add")

  # Call the Java remote function.
  obj_ref3 = add_function.remote(1, 2)
  assert ray.get(obj_ref3) == 3

Java calling Python#

Suppose we have a Python module as follows:

# /path/to/the_dir/ray_demo.py

import ray

@ray.remote
class Counter(object):
  def __init__(self):
      self.value = 0

  def increment(self):
      self.value += 1
      return self.value

@ray.remote
def add(a, b):
    return a + b

Note

The function or class should be decorated by @ray.remote.

Then, in Java, we can call the above Python remote function, or create an actor from the above Python class.

package io.ray.demo;

import io.ray.api.ObjectRef;
import io.ray.api.PyActorHandle;
import io.ray.api.Ray;
import io.ray.api.function.PyActorClass;
import io.ray.api.function.PyActorMethod;
import io.ray.api.function.PyFunction;
import org.testng.Assert;

public class JavaCallPythonDemo {

  public static void main(String[] args) {
    // Set the code-search-path to the directory of your `ray_demo.py` file.
    System.setProperty("ray.job.code-search-path", "/path/to/the_dir/");
    Ray.init();

    // Define a Python class.
    PyActorClass actorClass = PyActorClass.of(
        "ray_demo", "Counter");

    // Create a Python actor and call actor method.
    PyActorHandle actor = Ray.actor(actorClass).remote();
    ObjectRef objRef1 = actor.task(
        PyActorMethod.of("increment", int.class)).remote();
    Assert.assertEquals(objRef1.get(), 1);
    ObjectRef objRef2 = actor.task(
        PyActorMethod.of("increment", int.class)).remote();
    Assert.assertEquals(objRef2.get(), 2);

    // Call the Python remote function.
    ObjectRef objRef3 = Ray.task(PyFunction.of(
        "ray_demo", "add", int.class), 1, 2).remote();
    Assert.assertEquals(objRef3.get(), 3);

    Ray.shutdown();
  }
}

Cross-language data serialization#

The arguments and return values of ray call can be serialized & deserialized automatically if their types are the following:

Primitive data types

MessagePack

Python

Java

nil

None

null

bool

bool

Boolean

int

int

Short / Integer / Long / BigInteger

float

float

Float / Double

str

str

String

bin

bytes

byte[]

Basic container types

MessagePack

Python

Java

array

list

Array

Ray builtin types

ActorHandle

MessagePack	Python	Java
nil	None	null
bool	bool	Boolean
int	int	Short / Integer / Long / BigInteger
float	float	Float / Double
str	str	String
bin	bytes	byte[]

MessagePack	Python	Java
array	list	Array

Note

Be aware of float / double precision between Python and Java. If Java is using a float type to receive the input argument, the double precision Python data will be reduced to float precision in Java.
BigInteger can support a max value of 2^64-1, please refer to: msgpack/msgpack. If the value is larger than 2^64-1, then sending the value to Python will raise an exception.

The following example shows how to pass these types as parameters and how to return these types.

You can write a Python function which returns the input data:

# ray_serialization.py

import ray

@ray.remote
def py_return_input(v):
    return v

Then you can transfer the object from Java to Python, and back from Python to Java:

package io.ray.demo;

import io.ray.api.ObjectRef;
import io.ray.api.Ray;
import io.ray.api.function.PyFunction;
import java.math.BigInteger;
import org.testng.Assert;

public class SerializationDemo {

  public static void main(String[] args) {
    Ray.init();

    Object[] inputs = new Object[]{
        true,  // Boolean
        Byte.MAX_VALUE,  // Byte
        Short.MAX_VALUE,  // Short
        Integer.MAX_VALUE,  // Integer
        Long.MAX_VALUE,  // Long
        BigInteger.valueOf(Long.MAX_VALUE),  // BigInteger
        "Hello World!",  // String
        1.234f,  // Float
        1.234,  // Double
        "example binary".getBytes()};  // byte[]
    for (Object o : inputs) {
      ObjectRef res = Ray.task(
          PyFunction.of("ray_serialization", "py_return_input", o.getClass()),
          o).remote();
      Assert.assertEquals(res.get(), o);
    }

    Ray.shutdown();
  }
}

Cross-language exception stacks#

Suppose we have a Java package as follows:

package io.ray.demo;

import io.ray.api.ObjectRef;
import io.ray.api.Ray;
import io.ray.api.function.PyFunction;

public class MyRayClass {

  public static int raiseExceptionFromPython() {
    PyFunction<Integer> raiseException = PyFunction.of(
        "ray_exception", "raise_exception", Integer.class);
    ObjectRef<Integer> refObj = Ray.task(raiseException).remote();
    return refObj.get();
  }
}

and a Python module as follows:

# ray_exception.py

import ray

@ray.remote
def raise_exception():
    1 / 0

Then, run the following code:

# ray_exception_demo.py

import ray

with ray.init(job_config=ray.job_config.JobConfig(code_search_path=["/path/to/ray_exception"])):
  obj_ref = ray.cross_language.java_function(
        "io.ray.demo.MyRayClass",
        "raiseExceptionFromPython").remote()
  ray.get(obj_ref)  # <-- raise exception from here.

The exception stack will be:

Traceback (most recent call last):
  File "ray_exception_demo.py", line 9, in <module>
    ray.get(obj_ref)  # <-- raise exception from here.
  File "ray/python/ray/_private/client_mode_hook.py", line 105, in wrapper
    return func(*args, **kwargs)
  File "ray/python/ray/_private/worker.py", line 2247, in get
    raise value
ray.exceptions.CrossLanguageError: An exception raised from JAVA:
io.ray.api.exception.RayTaskException: (pid=61894, ip=172.17.0.2) Error executing task c8ef45ccd0112571ffffffffffffffffffffffff01000000
        at io.ray.runtime.task.TaskExecutor.execute(TaskExecutor.java:186)
        at io.ray.runtime.RayNativeRuntime.nativeRunTaskExecutor(Native Method)
        at io.ray.runtime.RayNativeRuntime.run(RayNativeRuntime.java:231)
        at io.ray.runtime.runner.worker.DefaultWorker.main(DefaultWorker.java:15)
Caused by: io.ray.api.exception.CrossLanguageException: An exception raised from PYTHON:
ray.exceptions.RayTaskError: ray::raise_exception() (pid=62041, ip=172.17.0.2)
  File "ray_exception.py", line 7, in raise_exception
    1 / 0
ZeroDivisionError: division by zero