[GitHub] [qpid-dispatch] ChugR commented on a change in pull request #805: Proposal for run-time lock validation

[GitBox <gi...@apache.org>]

ChugR commented on a change in pull request #805:
URL: https://github.com/apache/qpid-dispatch/pull/805#discussion_r465815463



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File path: docs/notes/RIPs/lock-validation.adoc
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+////
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License
+////
+
+= Mutex Locking Validation
+
+== Summary
+
+This RIP proposes a compile-time debug mechanism to ensure that thread
+locking is well behaved.
+
+== Introduction
+
+The Qpid Dispatch Router is a multi-threaded application.  These
+threads share state and use locks to ensure the consistency of that
+state.  The locking API is defined in
+include/qpid/dispatch/threading.h
+
+In general lock nesting (e.g. taking a lock while holding another) is
+not permitted.
+
+However in a few instances locks will nest. One example of permitted lock
+nesting is the Python lock (qd_python_lock()).  This lock must be held
+while a thread is running within the Python interpreter.  Occasionally
+the Python interpreter will invoke native C functions.  These
+functions may take addional locks, such as the global logging lock
+(log_lock).

Review comment:
       Log locking is used to keep the written log in strict chronological order. gettimeofday, vsnprintf, and write_log are the items that need to be locked but the code locks only a little more than that.
   It would be bad to have the logs out of order with respect to time of day.




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