how to show output from api function? - c++

Question

Sorry for basic question. I'm trying to show json in QPlainTextWidget. I have api function which have console output and contains all needed data. Looks like that:
int iperf_run_server(struct iperf_test *test)
{
int result, s, streams_accepted;
fd_set read_set, write_set;
struct iperf_stream *sp;
struct timeval now;
struct timeval* timeout;
......
if (test->json_output)
if (iperf_json_start(test) < 0)
return -1;
if (test->json_output) {
cJSON_AddItemToObject(test->json_start, "version", cJSON_CreateString(version));
cJSON_AddItemToObject(test->json_start, "system_info", cJSON_CreateString(get_system_info()));
} else if (test->verbose) {
iprintf(test, "%s\n", version);
iprintf(test, "%s", "");
fflush(stdout);
printf("%s\n", get_system_info());
}
.....
cleanup_server(test);
if (test->json_output) {
if (iperf_json_finish(test) < 0)
return -1;
}
....
return 0;
}
For now I have first thread with my gui, and second thread, contains class which run this function on a signal. All things works normally, but i'm not fully understand, how I can "stop" iperf_run_server for "reading/buffering" output, without any changes in api.

Answer 1

The simplest thing to do would be to collect each message in a string, and emit a signal from the object running in the second thread. You can connect that signal to a slot in an object in the GUI thread.A zero-timeout timer is invoked each time the event loop is done processing other events - it is a useful mechanism to leverage to run things "continuously".
For example:
#include <QApplication>
#include <QPlainTextEdit>
#include <QThread>
#include <QBasicTimer>
#include <QTextStream>
//! A thread that's always safe to destruct.
class Thread : public QThread {
private:
// This is a final class.
using QThread::run;
public:
Thread(QObject * parent = 0) : QThread(parent) {}
~Thread() {
quit();
wait();
}
};
class IperfTester : public QObject {
Q_OBJECT
struct Test { int n; Test(int n_) : n(n_) {} };
QList<Test> m_tests;
QBasicTimer m_timer;
public:
IperfTester(QObject * parent = 0) : QObject(parent) {
for (int i = 0; i < 50; ++i) m_tests << Test(i+1);
}
//! Run the tests. This function is thread-safe.
Q_SLOT void runTests() {
QMetaObject::invokeMethod(this, "runTestsImpl");
}
Q_SIGNAL void message(const QString &);
private:
Q_INVOKABLE void runTestsImpl() {
m_timer.start(0, this);
}
void timerEvent(QTimerEvent * ev) {
if (ev->timerId() != m_timer.timerId()) return;
if (m_tests.isEmpty()) {
m_timer.stop();
return;
}
runTest(m_tests.first());
m_tests.removeFirst();
}
void runTest(Test & test) {
// do the work
QString msg;
QTextStream s(&msg);
s << "Version:" << "3.11" << "\n";
s << "Number:" << test.n << "\n";
emit message(msg);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QPlainTextEdit log;
// This order is important: the thread must be defined after the object
// to be moved into the thread.
IperfTester tester;
Thread thread;
tester.moveToThread(&thread);
thread.start();
log.connect(&tester, SIGNAL(message(QString)), SLOT(appendPlainText(QString)));
log.show();
tester.runTests();
return a.exec();
// Here, the thread is stopped and destructed first, following by a now threadless
// tester. It would be an error if the tester object was destructed while its
// thread existed (even if it was stopped!).
}
#include "main.moc"