Add simple parallel computation library.

(imported from commit bd17f16c1645f5bb20e0b5e0799948c7f05fede0)

zephyr/lib/parallel.py

@@ -0,0 +1,71 @@
+import os
+import signal
+import pty
+import sys
+import errno
+
+def run_parallel(job, data, threads=6):
+    pids = {}
+
+    def wait_for_one():
+        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, e:
+                if e.errno != errno.EBADF:
+                    raise
+            sys.stdin = open("/dev/null", "r")
+            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, e:
+            if e.errno == errno.ECHILD:
+                break
+            else:
+                raise
+
+if __name__ == "__main__":
+    # run some unit tests
+    import random
+    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):
+        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
+