Constructing a Task from C Code#
Workflows can incorporate functions written in different languages, for example when a compiled C function is used to optimize performance. This example demonstrates how to construct a Lepton from a compiled C function.
Prerequisite#
Writing a Covalent lepton for a C function presupposes that you have a compiled C function that you want to call from within a Python session. This example creates a simple C program for that purpose.
Write C source and header files for the program:
[26]:
c_source = """
#include "test.h"
void test_entry(int x, int *y, int *z)
{
*y += x;
*z = 5;
}
"""
c_header = """
void test_entry(int x, int *y, int *z);
"""
with open("test.c", "w") as f:
f.write(c_source)
with open("test.h", "w") as f:
f.write(c_header)
Compile the C source into a shared library:
[27]:
!gcc -shared -fPIC -o libtest.so test.c
Procedure#
Construct a task that interfaces with the compiled function using a Covalent lepton object:
[29]:
import covalent as ct
from ctypes import POINTER, c_int32
import os
library_path = os.path.join(os.getcwd(),"libtest.so")
task = ct.Lepton(
language = "C",
library_name = library_path,
function_name = "test_entry",
argtypes = [ # Type conversion info required by the lepton object
(c_int32, ct.Lepton.INPUT),
(POINTER(c_int32), ct.Lepton.INPUT_OUTPUT),
(POINTER(c_int32), ct.Lepton.OUTPUT)
]
)
Use the lepton in the context of a lattice:
[30]:
@ct.lattice
def workflow(x: int, y: int) -> int:
return task(x, y)
dispatch_id = ct.dispatch(workflow)(1, 2)
result = ct.get_result(dispatch_id, wait=True)
print(result.result)
(3, 5)
Note that the return values consist of input-output and output-only variables. Output-only variables can only be scalars, since there is no way to to determine an output-only variable’s array size. To return an array, declare it as an input-output variable and initialize it appropriately before passing it to the lepton.