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From "Joseph Wu" <>
Subject Re: Review Request 39949: Document and simplify libprocess initialization synchronization logic.
Date Wed, 04 Nov 2015 20:24:05 GMT

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(Updated Nov. 4, 2015, 12:24 p.m.)

Review request for mesos, Benjamin Hindman, Joris Van Remoortere, and Neil Conway.


Renamed variables to more closely reflect their purpose.  Negated `initializing` to `initialize_complete`.
Did some manual tests.

Repository: mesos

Description (updated)

* Renamed `initialized` to `initialize_started`.
* Renamed `initializing` to `initialize_complete`.
* Removed the (2) condition, described below: 

The initialization synchronization logic contains three conditions, which check:
1) Was `initialize` called and is it done?
2) Was `initialize` called and is it not done?
3) Are you the first to call `initialize`?

Condition (3) uses `compare_exchange_strong` between `initialized` and `false`.  This returns
`true` (and sets `initialized` to true) iff the caller is the first to reach that expression.

The second simultaneous caller of `initialize` will either satisify condition (2) or (3) and
then wait on `initializing`.  For the second caller, (2) and (3) are identical because `compare_exchange_strong`
between `true` and `false` will always return false, thereby putting the second caller into
the waiting loop.

Diffs (updated)

  3rdparty/libprocess/src/process.cpp a94712b9ac3b60fb047b3a5a4d84a56fa4d02313 


Testing (updated)

`make check`

Replaced `process::initialize();` in `3rdparty/libprocess/src/tests/main.cpp` with:

  const size_t numThreads = 50;

  std::thread* runningThreads[numThreads];

  // Create additional threads.
  for (size_t i = 0; i < numThreads; i++) {
    runningThreads[i] = new std::thread([]() {

  for (size_t i = 0; i < numThreads; i++) {
    delete runningThreads[i];
(Also added `#include <thread>` to the header).

Rebuilt `libprocess-tests` with the modification and ran it a few times.


Joseph Wu

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