parallel: Remove run_parallel.

This was a broken abstraction that returned to its caller within
multiple forked processes on exceptions, and encouraged ignoring the
error code (as all of its callers did).

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

docs/testing/linters.md

@@ -126,9 +126,7 @@ eslint, and other home grown tools.
 You can find the source code [here](https://github.com/zulip/zulip/blob/master/tools/lint).
 
 In order for our entire lint suite to run in a timely fashion, the `lint`
-script performs several lint checks in parallel by forking out subprocesses.  This mechanism
-is still evolving, but you can look at the method `run_parallel` to get the
-gist of how it works.
+script performs several lint checks in parallel by forking out subprocesses.
 
 Note that our project does custom regex-based checks on the code, and we
 also customize how we call pyflakes and pycodestyle (pep8).  The code for these

tools/coveragerc

@@ -32,7 +32,6 @@ omit =
     zerver/lib/test_runner.py
     # Has its own independent test suite
     zerver/openapi/python_examples.py
-    zerver/lib/parallel.py
     # Debugging tools that don't lend themselves well to unit tests
     zerver/lib/debug.py
     # Part of provisioning/populate_db

tools/test-backend

@@ -91,7 +91,6 @@ not_yet_fully_covered = [
     'zerver/lib/logging_util.py',
     'zerver/lib/migrate.py',
     'zerver/lib/outgoing_webhook.py',
-    'zerver/lib/parallel.py',
     'zerver/lib/profile.py',
     'zerver/lib/queue.py',
     'zerver/lib/sqlalchemy_utils.py',

zerver/lib/parallel.py

@@ -1,74 +0,0 @@
-import errno
-import os
-import pty
-import sys
-from typing import Callable, Dict, Iterable, Iterator, Tuple, TypeVar
-
-JobData = TypeVar('JobData')
-
-def run_parallel(job: Callable[[JobData], int],
-                 data: Iterable[JobData],
-                 threads: int=6) -> Iterator[Tuple[int, JobData]]:
-    pids: Dict[int, JobData] = {}
-
-    def wait_for_one() -> Tuple[int, JobData]:
-        while True:
-            try:
-                (pid, status) = os.wait()
-                return status, pids.pop(pid)
-            except KeyError:
-                pass
-
-    for item in data:
-        pid = os.fork()
-        if pid == 0:
-            sys.stdin.close()
-            try:
-                os.close(pty.STDIN_FILENO)
-            except OSError as e:
-                if e.errno != errno.EBADF:
-                    raise
-            sys.stdin = open("/dev/null")
-            os._exit(job(item))
-
-        pids[pid] = item
-        threads = threads - 1
-
-        if threads == 0:
-            (status, item) = wait_for_one()
-            threads += 1
-            yield (status, item)
-            if status != 0:
-                # Stop if any error occurred
-                break
-
-    while True:
-        try:
-            (status, item) = wait_for_one()
-            yield (status, item)
-        except OSError as e:
-            if e.errno == errno.ECHILD:
-                break
-            else:
-                raise
-
-if __name__ == "__main__":
-    # run some unit tests
-    import time
-    jobs = [10, 19, 18, 6, 14, 12, 8, 2, 1, 13, 3, 17, 9, 11, 5, 16, 7, 15, 4]
-    expected_output = [6, 10, 12, 2, 1, 14, 8, 3, 18, 19, 5, 9, 13, 11, 4, 7, 17, 16, 15]
-
-    def wait_and_print(x: int) -> int:
-        time.sleep(x * 0.1)
-        return 0
-
-    output = []
-    for (status, job) in run_parallel(wait_and_print, jobs):
-        output.append(job)
-    if output == expected_output:
-        print("Successfully passed test!")
-    else:
-        print("Failed test!")
-        print(jobs)
-        print(expected_output)
-        print(output)