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Erik Boasson a652ecb78e ensure delivery of writes immediately following pub match event (#165)
A long-standing bug of Cyclone is that a sample written immediately
after a publication-matched event may never arrive at the reader that
was just matched.  This happened because the reader need not have
completed discovery of the writer by the time the writer discovers the
reader, at which point the reader ignores the sample because it either
doesn't know the writer at all, or it hasn't yet seen a Heartbeat from
it.

That Heartbeat arrives shortly after, but by then it is too late: the
reader slaves decides to accept the next sample to be written by the
writer.  (It has no choice, really: either you risk losing some data, or
you will be requesting all historical data, which is empathically not
what a volatile reader is about ...)

A related issue is the handling of historical data for transient-local
readers: it used to deliver this out-of-order, but that is firstly
against the specification, and secondly, against reasonable expectations
of those who use DDS as a mere publish-subscribe messaging system.  To
add insult to injury, it didn't completely handle some reordering issues
with disposes ...

This commit changes the way writers respond to a request for
retransmission from volatile proxy readers and the way the
in-sync/out-of-sync setting of a reader with respect to a proxy-writer
is used.  The first makes it safe for a Cyclone reader to ask a Cyclone
writer for all data (all these details not being covered in the specs it
errs on the reasonable side for other vendors, but that may cause the
data loss mentioned above): the writer simply send a Gap message to the
reader for all the sequence numbers prior to the matching.

The second changes the rule for switching from out-of-sync to in-sync:
that transition is now simply once the next sequence number to be
delivered to the reader equals the next sequence number that will be
delivered directly from the proxy writer object to all readers.  (I.e.,
a much more intuitive notion than reaching some seemingly arbitrary
sequence number.)

To avoid duplicates the rule for delivery straight from a proxy writer
has changed: where samples were delivered from the proxy writer to all
matching readers, they are now delivered only to the matching readers
that are in-sync.  To avoid ordering problems, the idea that historical
data can be delivered through the asynchronous delivery path even when
the regular data goes through the synchronous delivery path has been
abandoned.  All data now always follows the same path.

As these same mechanisms are used for getting historical data into
transient-local readers, the ordering problem for the historical data
also disappeared.

The test stuff in src/core/xtests/initsampledeliv covers a lot of the
interesting cases: data published before the existene of a reader, after
it, mixes of volatile and transient-local.  Running them takes quite a
bit of time, and they are not yet integrated in the CI builds (if ever,
because of that time).

Note: the "conservative built-in startup" option has been removed,
because it really makes no sense to keep a vague compatibility option
added a decade ago "just in case" that has never been used ...

Note: the workaround in the src/mpt/tests/basic/procs/hello.c (use
transient-local to ensure delivery of data) has been removed, as has
been its workaround for the already-fixed #146.

Signed-off-by: Erik Boasson <eb@ilities.com>
2019-05-29 13:20:37 +02:00
docs/dev Add support for FreeRTOS and lwIP (#166) 2019-05-23 14:27:56 +02:00
notes add some diagrams related to the data path 2018-07-04 15:59:55 +02:00
performance some minor improvements to the throughput test scripting 2019-01-22 09:15:18 +01:00
ports/freertos-posix Add support for FreeRTOS and lwIP (#166) 2019-05-23 14:27:56 +02:00
src ensure delivery of writes immediately following pub match event (#165) 2019-05-29 13:20:37 +02:00
vdds-xcode/vdds-xcode.xcodeproj Initial contribution 2018-04-10 17:03:59 +02:00
.gitignore Fix build with openJDK-10 2018-06-23 21:51:21 +02:00
.gitmodules Initial contribution 2018-04-10 17:03:59 +02:00
.travis.yml Add Coverity Scan target to .travis.yml 2019-05-24 07:42:48 +02:00
appveyor.yml enable expensive checks in CI builds 2019-03-23 15:40:29 +01:00
conanfile.txt Require OpenSSL by default and add list it as a dependency for Conan 2019-02-01 10:39:49 +01:00
CONTRIBUTING.md Add README 2018-04-24 10:07:55 +02:00
LICENSE Initial contribution 2018-04-10 17:03:59 +02:00
NOTICE.md Add getopt 1.5 3rd party dependency 2018-05-08 10:18:52 +02:00
README.md Editing of README and next-steps following review comments 2019-02-16 08:54:17 +01:00

Eclipse Cyclone DDS

Eclipse Cyclone DDS is by far the most performant and robust DDS implementation available on the market. Moreover, Cyclone DDS is developed completely in the open as an Eclipse IoT project (see eclipse-cyclone-dds).

Getting Started

Building Eclipse Cyclone DDS

In order to build Cyclone DDS you need a Linux, Mac or Windows 10 machine with the following installed on your host:

  • CMake, version 3.7 or later. (Version 3.6 should work but you will have to edit the cmake_minimum_required version and may have to disable building the tests.)
  • OpenSSL, preferably version 1.1 or later. If you wish, you can build without support for OpenSSL by setting DDSC_ENABLE_OPENSSL to FALSE on the cmake command line (i.e., cmake -DDDSC_ENABLE_OPENSSL=FALSE ../src). In that, there is no need to have openssl available.
  • Java JDK, version 8 or later, e.g., OpenJDK 11.
  • Apache Maven, version 3.5 or later.

The Java-based components are the preprocessor and a configurator tool. The run-time libraries are pure C code, so there is no need to have Java available on "target" machines.

To obtain Eclipse Cyclone DDS, do

$ git clone https://github.com/eclipse-cyclonedds/cyclonedds.git 
$ cd cyclonedds
$ mkdir build

Depending on whether you want to develop applications using Cyclone DDS or contribute to it you can follow different procedures

For application developers

To build and install the required libraries needed to develop your own applications using Cyclone DDS requires a few simple steps. There are some small differences between Linux and macOS on the one hand, and Windows on the other. For Linux or macOS:

$ cd build
$ cmake -DCMAKE_INSTALL_PREFIX=<install-location> ../src
$ cmake --build .

and for Windows:

$ cd build
$ cmake -G "<generator-name>" -DCMAKE_INSTALL_PREFIX=<install-location> ../src
$ cmake --build .

where you should replace <install-location> by the directory under which you would like to install Cyclone DDS and <generator-name> by one of the ways CMake generators offer for generating build files. For example, "Visual Studio 15 2017 Win64" would target a 64-bit build using Visual Studio 2017.

To install it after a successful build, do:

$ cmake --build . --target install

which will copy everything to:

  • <install-location>/lib
  • <install-location>/bin
  • <install-location>/include/ddsc
  • <install-location>/share/CycloneDDS
  • <install-location>/etc/CycloneDDS

Depending on the installation location you may need administrator privileges.

At this point you are ready to use Eclipse Cyclone DDS in your own projects.

Note that the default build type is a release build with debug information included (RelWithDebInfo), which is generally the most convenient type of build to use from applications because of a good mix between performance and still being able to debug things. If you'd rather have a Debug or pure Release build, set CMAKE_BUILD_TYPE accordingly.

Contributing to Eclipse Cyclone DDS

We very much welcome all contributions to the project, whether that is questions, examples, bug fixes, enhancements or improvements to the documentation, or anything else really. When considering contributing code, it might be good to know that build configurations for Travis CI and AppVeyor are present in the repository and that there is a test suite using CTest and CUnit that can be built locally if desired. To build it, set the cmake variable BUILD_TESTING to on when configuring, e.g.:

$ cd build
$ cmake -DCMAKE_BUILD_TYPE=Debug -DBUILD_TESTING=ON ../src
$ cmake --build .
$ ctest

Such a build requires the presence of CUnit. You can install this yourself, or you can choose to instead rely on the Conan packaging system that the CI build infrastructure also uses. In that case, install Conan and do:

$ conan install ..

in the build directory prior to running cmake. For Windows, depending on the generator, you might also need to add switches to select the architecture and build type, e.g., conan install -s arch=x86_64 -s build_type=Debug .. This will automatically download and/or build CUnit (and, at the moment, OpenSSL).

Documentation

The documentation is still rather limited, and at the moment only available in the sources (in the form of restructured text files in src/docs and Doxygen comments in the header files), or as a PDF. The intent is to automate the process of building the documentation and have them available in more convenient formats and in the usual locations.

Performance

Median small message throughput measured using the Throughput example between two Intel(R) Xeon(R) CPU E3-1270 V2 @ 3.50GHz (that's 2012 hardware ...) running Linux 3.8.13-rt14.20.el6rt.x86_64, connected via a quiet GbE and when using gcc-6.2.0 for a default (i.e., "RelWithDebInfo") build is:

Throughput

This is with the subscriber in polling mode. Listener mode is marginally slower; using a waitset the message rate for minimal size messages drops to 600k sample/s in synchronous delivery mode and about 750k samples/s in asynchronous delivery mode. The configuration is an out-of-the-box configuration, tweaked only to increase the high-water mark for the reliability window on the writer side. For details, see the scripts in the performance directory and the data.

There is some data on roundtrip latency below.

Building and Running the Roundtrip Example

We will show you how to build and run an example program that measures latency. The examples are built automatically when you build Cyclone DDS, so you don't need to follow these steps to be able to run the program, it is merely to illustrate the process.

$ cd cyclonedds/src/examples/roundtrip
$ mkdir build
$ cd build
$ cmake ..
$ make

On one terminal start the application that will be responding to pings:

$ ./RoundtripPong

On another terminal, start the application that will be sending the pings:

$ ./RoundtripPing 0 0 0 
# payloadSize: 0 | numSamples: 0 | timeOut: 0
# Waiting for startup jitter to stabilise
# Warm up complete.
# Round trip measurements (in us)
#             Round trip time [us]                           Write-access time [us]       Read-access time [us]
# Seconds     Count   median      min      99%      max      Count   median      min      Count   median      min
    1     28065       17       16       23       87      28065        8        6      28065        1        0
    2     28115       17       16       23       46      28115        8        6      28115        1        0
    3     28381       17       16       22       46      28381        8        6      28381        1        0
    4     27928       17       16       24      127      27928        8        6      27928        1        0
    5     28427       17       16       20       47      28427        8        6      28427        1        0
    6     27685       17       16       26       51      27685        8        6      27685        1        0
    7     28391       17       16       23       47      28391        8        6      28391        1        0
    8     27938       17       16       24       63      27938        8        6      27938        1        0
    9     28242       17       16       24      132      28242        8        6      28242        1        0
   10     28075       17       16       23       46      28075        8        6      28075        1        0

The numbers above were measured on Mac running a 4.2 GHz Intel Core i7 on December 12th 2018. From these numbers you can see how the roundtrip is very stable and the minimal latency is now down to 17 micro-seconds (used to be 25 micro-seconds) on this HW.

Trademarks

  • "Eclipse Cyclone DDS" and "Cyclone DDS" are trademarks of the Eclipse Foundation.

  • "DDS" is a trademark of the Object Management Group, Inc.