OSError: [Errno 24] Too many open files when RandomForestRegressor has 140 estimators

[ollieglass]

Here's a loop that fits and compiles trees, stepping up the number of estimators each time:

from sklearn import datasets, ensemble
import compiledtrees

data = datasets.load_boston()
X, y = data.data, data.target

for i in range(20, 250, 20):
    print(i)

    model = ensemble.RandomForestRegressor(n_jobs=4, n_estimators=i)
    model.fit(X, y)

    model = compiledtrees.CompiledRegressionPredictor(model)

    h = model.predict(X)

It crashes on 140:

$ python test_script.py 
20
40
60
80
100
120
140
Traceback (most recent call last):
  File "/Users/ollieglass/code/test_compiled_trees/lib/python3.5/site-packages/joblib/_parallel_backends.py", line 344, in __call__
    return self.func(*args, **kwargs)
  File "/Users/ollieglass/code/test_compiled_trees/lib/python3.5/site-packages/joblib/parallel.py", line 131, in __call__
    return [func(*args, **kwargs) for func, args, kwargs in self.items]
  File "/Users/ollieglass/code/test_compiled_trees/lib/python3.5/site-packages/joblib/parallel.py", line 131, in <listcomp>
    return [func(*args, **kwargs) for func, args, kwargs in self.items]
  File "/Users/ollieglass/code/test_compiled_trees/lib/python3.5/site-packages/compiledtrees/code_gen.py", line 173, in _compile
    _call([CXX_COMPILER, cpp_f, "-c", "-fPIC", "-o", o_f.name, "-O3", "-pipe"])
  File "/Users/ollieglass/code/test_compiled_trees/lib/python3.5/site-packages/compiledtrees/code_gen.py", line 179, in _call
    shell=True, stdout=DEVNULL, stderr=DEVNULL)
  File "/usr/local/Cellar/python3/3.5.2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/subprocess.py", line 576, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/local/Cellar/python3/3.5.2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/subprocess.py", line 557, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/local/Cellar/python3/3.5.2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/subprocess.py", line 947, in __init__
    restore_signals, start_new_session)
  File "/usr/local/Cellar/python3/3.5.2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/subprocess.py", line 1454, in _execute_child
    errpipe_read, errpipe_write = os.pipe()
OSError: [Errno 24] Too many open files

This is on mac OS.

I haven't looked into workarounds - perhaps I can increase the number of files that can be open at once. But if there's a way to limit the open files in the library, that would probably be better.