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From:	"PAULUS, Raimund, TI-ABN" <Raimund DOT Paulus AT dillinger DOT biz>
To:	"'cygwin AT cygwin DOT com'" <cygwin AT cygwin DOT com>
Subject:	Problems using Qt5 and Apache Thrift
Thread-Topic:	Problems using Qt5 and Apache Thrift
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Date:	Wed, 25 Mar 2020 09:04:10 +0000
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Problems using Qt5 and Apache Thrift

For several months i use Apache Thrift 0.11.0 on Cygwin 2.5.2 for data transfer between Windows boxes and my Linux host. On the Windows boxes a C++-application serves as a client. The user makes some input on an ascii-interface (created with libwed) and sometimes data must be transferred between the pc and the Linux host.

Here is the program sequence on the windows client:

//------------------------------------------------------------------------------
program starts
step 1: make the connection to the Linux server (Apache Thrift)
step 2: user interface (ASCII)
step 3: data transfer PC <-> Linux-Host (Apache Thrift)
step 4: user interface (ASCII)
step 5: data transfer PC <-> Linux-Host (Apache Thrift)
...
...
...
step n: close the connection to the host (Apache Thrift)
program ends
//------------------------------------------------------------------------------

This works flawlessly.

Now i want to implement the interface parts with Qt 5. Here is the new program sequence:

//------------------------------------------------------------------------------
program starts
step 1: make the connection to the Linux server (Apache Thrift)
step 2: initialize Qt interface (create widgets, buttons, ...)
step 3: user interface (Qt)
step 4: data transfer PC <-> Linux-Host (Apache Thrift)
step 5: user interface (Qt)
step 6: data transfer PC <-> Linux-Host (Apache Thrift)
...
...
...
step n-1: end Qt app
step n: close the connection to the host (Apache Thrift)
program ends
//------------------------------------------------------------------------------

During step 2 the connection to the linux server is broken. You can see it with the netstat command. First error message arises in step 4:

"TSocket::write_partial() send() <Host: my_host Port: 9090>Broken pipe"

On a Linux box the client program runs perfectly.

On the windows box the program works, if i initalize Qt before the connection to the server is made (step 2 before step 1). But that is not acceptable for me, because afterwards other widgets and buttons are created and i can not close and create the connection at each point.

For the tests I used the examples from the Apache Thrift Tutorial. The service on the linux box is created from CppServer.cpp. The client in the original is CppClient.cpp. But I modified it for Qt. Here is the source for CppClient.cpp. The connection is broken after line 66.


  1 #include <stdio.h>
  2 #include <iostream>
  3
  4 #include <QApplication>
  5 #include <QWidget>
  6 #include <QString>
  7 #include <QMessageBox>
  8 #include <QPushButton>
  9
 10 #include <thrift/protocol/TBinaryProtocol.h>
 11 #include <thrift/transport/TSocket.h>
 12 #include <thrift/transport/TTransportUtils.h>
 13 #include <thrift/stdcxx.h>
 14
 15 #include "../gen-cpp/Calculator.h"
 16
 17 using namespace std;
 18 using namespace apache::thrift;
 19 using namespace apache::thrift::protocol;
 20 using namespace apache::thrift::transport;
 21
 22 using namespace tutorial;
 23 using namespace shared;
 24
 25 // function for messagebox
 26 void MsgBox(const char *msg)
 27 {
 28   QMessageBox box;
 29   box.setIcon(QMessageBox::Information);
 30   box.setText("Server Return");
 31   box.setInformativeText(QString::fromStdString(msg));
 32   box.setStandardButtons(QMessageBox::Ok);
 33   box.exec();
 34 }
 35
 36 int main(int argc, char **argv) {
 37
 38   //-------------------------------------------------------
 39   // connect to host before initialising Qt
 40   //-------------------------------------------------------
 41 printf("Connect to host \"NAZV\"with port 9090\n");
 42
 43 //  stdcxx::shared_ptr<TTransport> socket(new TSocket("localhost", 9090));
 44   stdcxx::shared_ptr<TTransport> socket(new TSocket("NAZV", 9090));
 45   stdcxx::shared_ptr<TTransport> transport(new TBufferedTransport(socket));
 46   stdcxx::shared_ptr<TProtocol> protocol(new TBinaryProtocol(transport));
 47   CalculatorClient client(protocol);
 48
 49   try {
 50     transport->open();
 51
 52     //------------------------------------------------------
 53     // initialising Qt after connect to host
 54     //------------------------------------------------------
 55 printf("Stop 1; Press <Enter> to continue"); getchar();
 56
 57     QApplication app(argc, argv);
 58     QString txt;
 59
 60 printf("Stop 2; Press <Enter> to continue"); getchar();
 61
 62     QWidget *w = new QWidget();
 63
 64 printf("Stop 3; Press <Enter> to continue"); getchar();
 65
 66     QPushButton *b_end = new QPushButton("End", w);
 67
 68 printf("Stop 4; Press <Enter> to continue"); getchar();
 69
 70     QObject::connect(b_end, SIGNAL(clicked()), &app, SLOT(quit()));
 71
 72 printf("Stop 5; Press <Enter> to continue"); getchar();
 73
 74     w->show();
 75
 76 printf("Stop 6; Press <Enter> to continue"); getchar();
 77
 78
 79     client.ping();
 80     MsgBox("ping()");
 81
 82     txt.clear();
 83     txt.append("1 + 1 = ");
 84     txt.append(QString::number(client.add(1, 1)));
 85     MsgBox(txt.toStdString().c_str());
 86
 87     Work work;
 88     work.op = Operation::DIVIDE;
 89     work.num1 = 1;
 90     work.num2 = 0;
 91
 92     try {
 93       client.calculate(1, work);
 94       MsgBox("Whoa? We can divide by zero!");
 95     } catch (InvalidOperation& io) {
 96       txt.clear();
 97       txt.append("InvalidOperation: ");
 98       txt.append(io.why.c_str());
 99       MsgBox(txt.toStdString().c_str());
100     }
101
102     work.op = Operation::SUBTRACT;
103     work.num1 = 15;
104     work.num2 = 10;
105     int32_t diff = client.calculate(1, work);
106     txt.clear();
107     txt.append("15 - 10 = ");
108     txt.append(QString::number(diff));
109     MsgBox(txt.toStdString().c_str());
110
111
112     app.exec();
113
114     transport->close();
115   } catch (TException& tx) {
116     cout << "ERROR: " << tx.what();
117   }
118
119 }


The result is the same on Cygwin 3.1.4 and Apache Thrift 0.12.0.

I would be very grateful for your help

Raimund Paulus
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