bpo-5001: More-informative multiprocessing error messages (#3079)

* Make error message more informative

Replace assertions in error-reporting code with more-informative version that doesn't cause confusion over where and what the error is.

* Additional clarification + get travis to check

* Change from SystemError to TypeError

As suggested in PR comment by @pitrou, changing from SystemError; TypeError appears appropriate.

* NEWS file installation; ACKS addition (will do my best to justify it by additional work)

* Making current AssertionErrors in multiprocessing more informative

* Blurb added re multiprocessing managers.py, queues.py cleanup

* Further multiprocessing cleanup - went through pool.py

* Fix two asserts in multiprocessing/util.py

* Most asserts in multiprocessing more informative

* Didn't save right version

* Further work on multiprocessing error messages

* Correct typo

* Correct typo v2

* Blasted colon... serves me right for trying to work on two things at once

* Simplify NEWS entry

* Update 2017-08-18-17-16-38.bpo-5001.gwnthq.rst

* Update 2017-08-18-17-16-38.bpo-5001.gwnthq.rst

OK, never mind.

* Corrected (thanks to pitrou) error messages for notify

* Remove extraneous backslash in docstring.

1 files changed, 12 insertions, 3 deletions

diff --git a/Lib/multiprocessing/heap.py b/Lib/multiprocessing/heap.py
index ee3ed55..566173a 100644
--- a/Lib/multiprocessing/heap.py
+++ b/Lib/multiprocessing/heap.py
@@ -211,7 +211,10 @@ class Heap(object):
         # synchronously sometimes later from malloc() or free(), by calling
         # _free_pending_blocks() (appending and retrieving from a list is not
         # strictly thread-safe but under cPython it's atomic thanks to the GIL).
-        assert os.getpid() == self._lastpid
+        if os.getpid() != self._lastpid:
+            raise ValueError(
+                "My pid ({0:n}) is not last pid {1:n}".format(
+                    os.getpid(),self._lastpid))
         if not self._lock.acquire(False):
             # can't acquire the lock right now, add the block to the list of
             # pending blocks to free
@@ -227,7 +230,10 @@ class Heap(object):
 
     def malloc(self, size):
         # return a block of right size (possibly rounded up)
-        assert 0 <= size < sys.maxsize
+        if size < 0:
+            raise ValueError("Size {0:n} out of range".format(size))
+        if sys.maxsize <= size:
+            raise OverflowError("Size {0:n} too large".format(size))
         if os.getpid() != self._lastpid:
             self.__init__()                     # reinitialize after fork
         with self._lock:
@@ -250,7 +256,10 @@ class BufferWrapper(object):
     _heap = Heap()
 
     def __init__(self, size):
-        assert 0 <= size < sys.maxsize
+        if size < 0:
+            raise ValueError("Size {0:n} out of range".format(size))
+        if sys.maxsize <= size:
+            raise OverflowError("Size {0:n} too large".format(size))
         block = BufferWrapper._heap.malloc(size)
         self._state = (block, size)
         util.Finalize(self, BufferWrapper._heap.free, args=(block,))