lib/oe/utils: Add utils function for multiprocess execution

Our usage of multitprocessing is problematic. In particular, there is a bug
in python 2.7 multiprocessing where signals are not handled until command
completion instead of immediately.

This factors the multiprocess code into a function which is enhanced with
a workaround to ensure immediate signal handling and also better SIGINT
handling which should happen in the parent, not the children to ensure
clean exits. The workaround for the signals is being added to the core
bb.utils function so it can benefit all users.

package_manager is then converted to use the new code.

(From OE-Core rev: 72d153a3a90d31d9f4e41d77da24e44ccb33c56e)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/package_manager.py

@@ -7,6 +7,7 @@ import multiprocessing
 import re
 import bb
 import tempfile
+import oe.utils
 
 
 # this can be used by all PM backends to create the index files in parallel
@@ -116,16 +117,7 @@ class RpmIndexer(Indexer):
             bb.note("There are no packages in %s" % self.deploy_dir)
             return
 
-        nproc = multiprocessing.cpu_count()
-        pool = bb.utils.multiprocessingpool(nproc)
-        results = list(pool.imap(create_index, index_cmds))
-        pool.close()
-        pool.join()
-
-        for result in results:
-            if result is not None:
-                return(result)
-
+        oe.utils.multiprocess_exec(index_cmds, create_index)
 
 class OpkgIndexer(Indexer):
     def write_index(self):
@@ -161,15 +153,7 @@ class OpkgIndexer(Indexer):
             bb.note("There are no packages in %s!" % self.deploy_dir)
             return
 
-        nproc = multiprocessing.cpu_count()
-        pool = bb.utils.multiprocessingpool(nproc)
-        results = list(pool.imap(create_index, index_cmds))
-        pool.close()
-        pool.join()
-
-        for result in results:
-            if result is not None:
-                return(result)
+        oe.utils.multiprocess_exec(index_cmds, create_index)
 
 
 class DpkgIndexer(Indexer):
@@ -210,15 +194,7 @@ class DpkgIndexer(Indexer):
             bb.note("There are no packages in %s" % self.deploy_dir)
             return
 
-        nproc = multiprocessing.cpu_count()
-        pool = bb.utils.multiprocessingpool(nproc)
-        results = list(pool.imap(create_index, index_cmds))
-        pool.close()
-        pool.join()
-
-        for result in results:
-            if result is not None:
-                return(result)
+        oe.utils.multiprocess_exec(index_cmds, create_index)
 
 
 class PkgsList(object):

meta/lib/oe/utils.py

@@ -151,3 +151,32 @@ def execute_pre_post_process(d, cmds):
         if cmd != '':
             bb.note("Executing %s ..." % cmd)
             bb.build.exec_func(cmd, d)
+
+def multiprocess_exec(commands, function):
+    import signal
+    import multiprocessing
+
+    if not commands:
+        return []
+
+    def init_worker():
+        signal.signal(signal.SIGINT, signal.SIG_IGN)
+
+    nproc = min(multiprocessing.cpu_count(), len(commands))
+    pool = bb.utils.multiprocessingpool(nproc, init_worker)
+    imap = pool.imap(function, commands)
+
+    try:
+        results = list(imap)
+        pool.close()
+        pool.join()
+        results = []
+        for result in results:
+            if result is not None:
+                results.append(result)
+        return results
+
+    except KeyboardInterrupt:
+        pool.terminate()
+        pool.join()
+        raise