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 5 Comments

Configuring sendmail with GMail relay on Ubuntu 16.04

Posted by | Ubuntu | Tagged |

Previously I published post How I configured sendmail for PHP on Ubuntu Server 12.04 describing how to configure sendmail to use custom SMTP server. But after switching to Ubuntu 16.04 VPS my first idea was that I can use sendmail in its default configuration, but this idea was wrong, because while sendmail worked well with yandex.ru (some Russian mail server), for example, it did not work with GMail, because GMail did not accept the mail reporting ‘DSN: Service unavailable.‘ in /var/log/mail.log, see my post on Ubuntu Forum for more information. Now my second idea is that using GMail as sendmail relay will prevent GMail from rejecting my mail. Below I provided a short instruction on how to realize this successful idea.

Install the packages

apt-get install sendmail mailutils

mailutils allows to run mail command.

(more…)

23
10
17
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Fun with Bitcoin mining on a home Windows machine.

Posted by | BTC, Video cards, Windows | Tagged |

I have heard many times that there are a lot of Russian guys who build mining farms and earn money with cryptocurrencies. Who knows, probably cryptocurrencies are still only at the starting point of their growth, or probably it is too late to start mining, or as another alternative Russian government will forbid them, but anyway it was interesting for me, how much Bitcoins my home Windows computer with relatively old graphic card can mine.

I overclocked my GeForce GTX 750 graphics card a bit:

(more…)

03
10
17
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Exponential growth policy of std::vector

Posted by | C++ |

Once std::vector is filled (size() equals to capacity()), a subsequent push_back(…) results in an exponential expansion of the vector capacity. The following table shows that the expansion happens when the index reaches a power of two:

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index: 0, capacity: 1, address: 0x1fa6c20
index: 1, capacity: 2, address: 0x1fa6c40
index: 2, capacity: 4, address: 0x1fa6c20
index: 4, capacity: 8, address: 0x1fa6c60
index: 8, capacity: 16, address: 0x1fa6c90
index: 16, capacity: 32, address: 0x1fa6ce0
index: 32, capacity: 64, address: 0x1fa6d70
index: 64, capacity: 128, address: 0x1fa6e80
index: 128, capacity: 256, address: 0x1fa7090
index: 256, capacity: 512, address: 0x1fa74a0
index: 512, capacity: 1024, address: 0x1fa7cb0
index: 1024, capacity: 2048, address: 0x1fa8cc0
index: 2048, capacity: 4096, address: 0x1faacd0
index: 4096, capacity: 8192, address: 0x1faece0
index: 8192, capacity: 16384, address: 0x1fb6cf0
index: 16384, capacity: 32768, address: 0x1fc6d00
index: 32768, capacity: 65536, address: 0x1fe6d10
index: 65536, capacity: 131072, address: 0x2026d20
index: 131072, capacity: 262144, address: 0x20a6d30
index: 262144, capacity: 524288, address: 0x21a6d40
index: 524288, capacity: 1048576, address: 0x23a6d50
index: 1048576, capacity: 2097152, address: 0x27a6d60
index: 2097152, capacity: 4194304, address: 0x2fa6d70
index: 4194304, capacity: 8388608, address: 0x7f8e9225f010
index: 8388608, capacity: 16777216, address: 0x7f8e8e25e010
index: 16777216, capacity: 33554432, address: 0x7f8e8625d010
index: 33554432, capacity: 67108864, address: 0x7f8e7625c010
index: 67108864, capacity: 134217728, address: 0x7f8e5625b010
index: 134217728, capacity: 268435456, address: 0x7f8e1625a010
index: 268435456, capacity: 536870912, address: 0x7f8d96259010
index: 536870912, capacity: 1073741824, address: 0x7f8c96258010

(more…)

27
09
17
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How to erase an element with a reverse iterator from C++ container

Posted by | C++ |

The following C++ code demonstrates how to erase an element a reverse iterator points to:

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#include <iostream>
#include <set>
#include <cassert>
 
int main()
{
    std::set<int> set;
  
    set.insert(15);
  
    std::cout << set.size() << " ";
  
    auto ri = set.rbegin();
  
    auto i1 = --ri.base();
  
    auto i2 = --set.end();
  
    assert(i1 == i2);
  
    set.erase(i1);
  
    std::cout << set.size() << std::endl;
}

The output is ‘1 0’. The key point here is that the reverse iterator is an adaptor for reverse-order traversal that can be created from forward iterator with std::make_reverse_iterator.

18
09
17
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An example of how GCC thread sanitizer works.

Posted by | C++ |

The following simple code C++ example can be used for investigation of how GCC thread sanitizer works:

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#include <mutex>
#include <atomic>
#include <iostream>
#include <thread>
 
std::mutex mutex;
int a = 3;
const size_t size = 1000 * 1000;
std::atomic<int> b(1);
 
void testA()
{
    for (size_t counter = 0; counter < size; counter++)
    {
        ++b;
        std::unique_lock<std::mutex> lock(mutex);
        ++a;
    }
}
 
void testB()
{
    for (size_t counter = 0; counter < size; counter++)
    {
        --b;
        std::unique_lock<std::mutex> lock(mutex);
        --a;
    }
}
 
int main()
{
    std::thread t1(testA);
    std::thread t2(testB);
    t1.join();
    t2.join();
}

(more…)

31
08
17
 1 Comment

Multiple views with OsgQtQuick

Posted by | C++, QML, QT |

I wrote a sample application using OsgQtQuick that shows the Earth in two views:

with the following QML, that I copied from OsgQtQuick samples:

(more…)

28
08
17
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A sample C++ code demonstrating why int is not atomic

Posted by | C++ |

The code below demonstrates why it is not guaranteed that 4-byte value being written by another thread is read either as original or final, but it can be read “partially written”:

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static constexpr int offset=2;
alignas(64) char vars[64+4-offset];
static volatile unsigned * const p = reinterpret_cast<unsigned *>(&vars[64-offset]);
 
unsigned getVar()
{
    return *p;
}
 
void loop()
{
    while(true)
    {
        *p = -1;
        *p = 0;
    }
}
 
#include <thread>
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <map>
 
int main()
{
    std::thread thread(loop);
    std::map<unsigned,int> xs;
    for(int i=0;i<10000000;++i)
    {
        const auto x=getVar();
        ++xs[x];
    }
    for(const auto& x : xs)
        std::cout << std::setfill('0') << std::setw(8) << std::hex << x.first << ": " << std::dec << x.second << " times\n";
    std::exit(0); // exit, killing the thread without abnormal termination via std::terminate
}

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22
08
17
 2 Comments

Compiling the latest version of CMake from sources on Ubuntu

Posted by | Ubuntu |

I was unable to add QML resources to a QT Quick application with CMake 2.8 installed on my machine, so I built the latest version of CMake with the following commands:

cd ~/examples
mkdir tools
cd tools
mkdir install
tar -xf ~/Downloads/cmake-3.9.1.tar.gz
cd cmake-3.9.1/
./configure --prefix=/home/dmitry/examples/tools/install/
make -j4
make install

Now my QT application is compiled and run successfully:

~/examples/tools/install/bin/cmake ../../OsgQmlTest/ -DCMAKE_BUILD_TYPE=Debug -DCMAKE_MODULE_PATH=/home/user/3rdpart/osg/CMakeModules/ -DCMAKE_INSTALL_PREFIX=/home/dmitry/examples/install
make -j4
make install

(more…)

21
08
17
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Building OsgQtQuick on Ubuntu 14.04

Posted by | Ubuntu |

The following section in OsgQtQuick‘s CMakeLists.txt:

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find_package(OpenSceneGraph 3.0 REQUIRED
  osg
  osgQt
  osgDB
  osgGA
  osgManipulator
  osgUtil
  osgViewer
  osgText)

results in CMake searching for FindOpenSceneGraph.cmake file:

strace cmake ../../osgqtquick/ -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/home/dmitry/examples/install |& grep -i OpenSceneGraph
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access("/home/dmitry/examples/osgqtquick/cmake/FindOpenSceneGraph.cmake", R_OK) = -1 ENOENT (No such file or directory)
access("/usr/share/cmake-2.8/Modules/FindOpenSceneGraph.cmake", R_OK) = 0
access("/usr/share/cmake-2.8/Modules/FindOpenSceneGraph.cmake", R_OK) = 0
stat("/usr/share/cmake-2.8/Modules/FindOpenSceneGraph.cmake", {st_mode=S_IFREG|0644, st_size=7438, ...}) = 0
open("/usr/share/cmake-2.8/Modules/FindOpenSceneGraph.cmake", O_RDONLY) = 3
read(3, "# - Find OpenSceneGraph\n# This m"..., 8192) = 7438
read(3, "/* -*-c++-*- OpenSceneGraph - Co"..., 4096) = 3495
read(3, "/* -*-c++-*- OpenSceneGraph - Co"..., 8191) = 3495
  Could NOT find OpenSceneGraph (missing: OPENSCENEGRAPH_LIBRARIES
  OPENSCENEGRAPH_INCLUDE_DIR OSG_FOUND OSGQT_FOUND OSGDB_FOUND OSGGA_FOUND
  /usr/share/cmake-2.8/Modules/FindOpenSceneGraph.cmake:187 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
access("/usr/share/cmake-2.8/Modules/FindOpenSceneGraph.cmake", R_OK) = 0

(more…)

19
08
17
 4 Comments

Qt Quick Controls 2 has TableView but without the header yet

Posted by | QML, QT |

QT 5.13 supports SplitView and TableView but without TableHeader yet. Probably TableHeader can be implemented with the overlays. And there is an interesting example of implementation of table header with the source code.

The information provided below is outdated.

Qt Quick Controls 2 does not support TableView and looks like they are not going to support it, some notable missing features from Qt Quick Controls 1 also are Action, SplitView and TreeView, so the following QML code would not work:

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TableView {
 
    TableViewColumn {
        role: "time"
        title: qsTr("date/time:")
        width: parent.width - 30
    }
 
    TableViewColumn {
        role: "score"
        title: qsTr("result:")
        width: 30
    }
 
    model: boardModel.list
 
    ScrollIndicator.vertical: ScrollIndicator { }
}

But there is a solution with ListView, so there can be something like this:

(more…)

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