Implement concurrent execution of individual hooks

pre_commit/clientlib.py

@@ -56,6 +56,7 @@ MANIFEST_HOOK_DICT = cfgv.Map(
     cfgv.Optional('language_version', cfgv.check_string, 'default'),
     cfgv.Optional('log_file', cfgv.check_string, ''),
     cfgv.Optional('minimum_pre_commit_version', cfgv.check_string, '0'),
+    cfgv.Optional('require_serial', cfgv.check_bool, False),
     cfgv.Optional('stages', cfgv.check_array(cfgv.check_one_of(C.STAGES)), []),
     cfgv.Optional('verbose', cfgv.check_bool, False),
 )

pre_commit/languages/docker.py

@@ -97,4 +97,8 @@ def run_hook(prefix, hook, file_args):  # pragma: windows no cover
 
     entry_tag = ('--entrypoint', entry_exe, docker_tag(prefix))
     cmd = docker_cmd() + entry_tag + cmd_rest
-    return xargs(cmd, file_args)
+    return xargs(
+        cmd,
+        file_args,
+        target_concurrency=helpers.target_concurrency(hook),
+    )

pre_commit/languages/docker_image.py

@@ -16,4 +16,8 @@ install_environment = helpers.no_install
 def run_hook(prefix, hook, file_args):  # pragma: windows no cover
     assert_docker_available()
     cmd = docker_cmd() + helpers.to_cmd(hook)
-    return xargs(cmd, file_args)
+    return xargs(
+        cmd,
+        file_args,
+        target_concurrency=helpers.target_concurrency(hook),
+    )

pre_commit/languages/golang.py

@@ -81,4 +81,8 @@ def install_environment(prefix, version, additional_dependencies):
 
 def run_hook(prefix, hook, file_args):
     with in_env(prefix):
-        return xargs(helpers.to_cmd(hook), file_args)
+        return xargs(
+            helpers.to_cmd(hook),
+            file_args,
+            target_concurrency=helpers.target_concurrency(hook),
+        )

pre_commit/languages/helpers.py

@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+import multiprocessing
 import shlex
 
 from pre_commit.util import cmd_output
@@ -45,3 +46,11 @@ def basic_healthy(prefix, language_version):
 
 def no_install(prefix, version, additional_dependencies):
     raise AssertionError('This type is not installable')
+
+
+def target_concurrency(hook):
+    if hook['require_serial']:
+        return 1
+    else:
+        # TODO: something smart!
+        return multiprocessing.cpu_count()

pre_commit/languages/node.py

@@ -71,4 +71,8 @@ def install_environment(prefix, version, additional_dependencies):
 
 def run_hook(prefix, hook, file_args):
     with in_env(prefix, hook['language_version']):
-        return xargs(helpers.to_cmd(hook), file_args)
+        return xargs(
+            helpers.to_cmd(hook),
+            file_args,
+            target_concurrency=helpers.target_concurrency(hook),
+        )

pre_commit/languages/python.py

@@ -127,7 +127,11 @@ def py_interface(_dir, _make_venv):
 
     def run_hook(prefix, hook, file_args):
         with in_env(prefix, hook['language_version']):
-            return xargs(helpers.to_cmd(hook), file_args)
+            return xargs(
+                helpers.to_cmd(hook),
+                file_args,
+                target_concurrency=helpers.target_concurrency(hook),
+            )
 
     def install_environment(prefix, version, additional_dependencies):
         additional_dependencies = tuple(additional_dependencies)

pre_commit/languages/ruby.py

@@ -126,4 +126,8 @@ def install_environment(
 
 def run_hook(prefix, hook, file_args):  # pragma: windows no cover
     with in_env(prefix, hook['language_version']):
-        return xargs(helpers.to_cmd(hook), file_args)
+        return xargs(
+            helpers.to_cmd(hook),
+            file_args,
+            target_concurrency=helpers.target_concurrency(hook),
+        )

pre_commit/languages/rust.py

@@ -91,4 +91,8 @@ def install_environment(prefix, version, additional_dependencies):
 
 def run_hook(prefix, hook, file_args):
     with in_env(prefix):
-        return xargs(helpers.to_cmd(hook), file_args)
+        return xargs(
+            helpers.to_cmd(hook),
+            file_args,
+            target_concurrency=helpers.target_concurrency(hook),
+        )

pre_commit/languages/script.py

@@ -13,4 +13,8 @@ install_environment = helpers.no_install
 def run_hook(prefix, hook, file_args):
     cmd = helpers.to_cmd(hook)
     cmd = (prefix.path(cmd[0]),) + cmd[1:]
-    return xargs(cmd, file_args)
+    return xargs(
+        cmd,
+        file_args,
+        target_concurrency=helpers.target_concurrency(hook),
+    )

pre_commit/languages/swift.py

@@ -53,4 +53,8 @@ def install_environment(
 
 def run_hook(prefix, hook, file_args):  # pragma: windows no cover
     with in_env(prefix):
-        return xargs(helpers.to_cmd(hook), file_args)
+        return xargs(
+            helpers.to_cmd(hook),
+            file_args,
+            target_concurrency=helpers.target_concurrency(hook),
+        )

pre_commit/languages/system.py

@@ -11,4 +11,8 @@ install_environment = helpers.no_install
 
 
 def run_hook(prefix, hook, file_args):
-    return xargs(helpers.to_cmd(hook), file_args)
+    return xargs(
+        helpers.to_cmd(hook),
+        file_args,
+        target_concurrency=helpers.target_concurrency(hook),
+    )

pre_commit/xargs.py

@@ -1,8 +1,11 @@
 from __future__ import absolute_import
 from __future__ import unicode_literals
 
+import contextlib
+import multiprocessing.pool
 import sys
 
+import concurrent.futures
 import six
 
 from pre_commit import parse_shebang
@@ -65,12 +68,23 @@ def partition(cmd, varargs, _max_length=None):
     return tuple(ret)
 
 
+@contextlib.contextmanager
+def _threadpool(size):
+    pool = multiprocessing.pool.ThreadPool(size)
+    try:
+        yield pool
+    finally:
+        pool.terminate()
+
+
 def xargs(cmd, varargs, **kwargs):
     """A simplified implementation of xargs.
 
     negate: Make nonzero successful and zero a failure
+    target_concurrency: Target number of partitions to run concurrently
     """
     negate = kwargs.pop('negate', False)
+    target_concurrency = kwargs.pop('target_concurrency', 1)
     retcode = 0
     stdout = b''
     stderr = b''
@@ -80,10 +94,17 @@ def xargs(cmd, varargs, **kwargs):
     except parse_shebang.ExecutableNotFoundError as e:
         return e.to_output()
 
-    for run_cmd in partition(cmd, varargs, **kwargs):
-        proc_retcode, proc_out, proc_err = cmd_output(
-            *run_cmd, encoding=None, retcode=None
-        )
+    # TODO: teach partition to intelligently target our desired concurrency
+    # while still respecting max_length.
+    partitions = partition(cmd, varargs, **kwargs)
+
+    def run_cmd_partition(run_cmd):
+        return cmd_output(*run_cmd, encoding=None, retcode=None)
+
+    with _threadpool(min(len(partitions), target_concurrency)) as pool:
+        results = pool.map(run_cmd_partition, partitions)
+
+    for proc_retcode, proc_out, proc_err in results:
         # This is *slightly* too clever so I'll explain it.
         # First the xor boolean table:
         #     T | F |

tests/repository_test.py

@@ -837,6 +837,7 @@ def test_manifest_hooks(tempdir_factory, store):
         'minimum_pre_commit_version': '0',
         'name': 'Bash hook',
         'pass_filenames': True,
+        'require_serial': False,
         'stages': [],
         'types': ['file'],
         'exclude_types': [],

tests/xargs_test.py

@@ -3,6 +3,7 @@ from __future__ import absolute_import
 from __future__ import unicode_literals
 
 import sys
+import time
 
 import mock
 import pytest
@@ -132,3 +133,20 @@ def test_xargs_retcode_normal():
 
     ret, _, _ = xargs.xargs(exit_cmd, ('0', '1'), _max_length=max_length)
     assert ret == 1
+
+
+def test_xargs_concurrency():
+    bash_cmd = ('bash', '-c')
+    print_pid = ('sleep 0.5 && echo $$',)
+
+    start = time.time()
+    ret, stdout, _ = xargs.xargs(
+        bash_cmd, print_pid * 5,
+        target_concurrency=5,
+        _max_length=len(' '.join(bash_cmd + print_pid)),
+    )
+    elapsed = time.time() - start
+    assert ret == 0
+    pids = stdout.splitlines()
+    assert len(pids) == 5
+    assert elapsed < 1