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diff --git a/blog/post/2016-09-24.html b/blog/post/2016-09-24.html deleted file mode 100644 index f3c95b2..0000000 --- a/blog/post/2016-09-24.html +++ /dev/null @@ -1,200 +0,0 @@ -<!DOCTYPE html><html><head> -<meta charset="utf-8"> -<meta name="viewport" content="width=device-width,initial-scale=1"> -<meta name="theme-color" content="#000000"> -<title>Chrisoft::Blog(r#"2-in-1")</title> -<meta name="description" content="«2-in-1» de spelunca ursae"> -<meta name="author" content="Chris Xiong"> -<script type="text/javascript" src="/panel.js"></script> -<script type="text/javascript" src="/themer.js"></script> -<script type="text/javascript" src="/blog/footnoter.js"></script> -<script type="text/javascript" src="/blog/aes-js.js"></script> -<script type="text/javascript" src="/blog/scrypt.js"></script> -<script type="text/javascript" src="/blog/sha256.js"></script> -<script type="text/javascript" src="/blog/decryptor.js"></script> -<link rel="stylesheet" type="text/css" href="/common.css"> -<link rel="stylesheet" type="text/css" href="/panel.css"> -<link rel="stylesheet" type="text/css" href="/theme0a.css" id="theme0a"> -<link rel="stylesheet" type="text/css" href="/theme0b.css" id="theme0b"> -<link rel="stylesheet" type="text/css" href="/theme1a.css" id="theme1a"> -<link rel="stylesheet" type="text/css" href="/theme1b.css" id="theme1b"> -<link rel="stylesheet" type="text/css" href="/theme2a.css" id="theme2a"> -<link rel="stylesheet" type="text/css" href="/theme2b.css" id="theme2b"> -<link rel="stylesheet" type="text/css" href="/theme3a.css" id="theme3a"> -<link rel="stylesheet" type="text/css" href="/theme3b.css" id="theme3b"> -<link rel="stylesheet" type="text/css" href="/blog/blogext.css"> -<script> -function ol() -{ - window.onresize=function() - { - if(window.innerWidth<768) - setupevents(); - else unsetevents(); - } - window.onresize(); - loadTheme(); - _decryptonload(); -} -</script> -</head> -<body onload="ol()" style="overflow-x:hidden;"> - <div id="panel" class="TText"> - <ul id="panellist"> - <li><a href="/"><h1>Chrisoft</h1></a></li> - <li><a href="/blog"><h2>Blog</h2></a></li> - <li><a href="#"><h3 id="title">2-in-1</h3></a></li> - <li><span>Tags</span> - <ul id="tagslist"> - <li><a href="/blog/list/devel/">devel</a></li><li><a href="/blog/list/qmidiplayer/">qmidiplayer</a></li><li><a href="/blog/list/c++/">c++</a></li><li><a href="/blog/list/qt/">qt</a></li></ul> - </li> - <li id="tocouter"> - <span>Table of Contents</span> - <ul id="tocroot"> - <li><a class="toctarg" href="#tocanch0">UPD 2016-10-28</a></li><li><ul class="tocnode"><li><a class="toctarg" href="#tocanch1">BUT THAT'S NOT THE END OF THE STORY.</a></li></ul></li><li><a class="toctarg" href="#tocanch2">UPD@2016-12-28</a></li></ul> - </li> - <li style="margin-left:-0.5em"><a id="prevp" href="2016-06-21.html">Prev post</a></li> - <li style="margin-left:-0.5em"><a id="nextp" href="2017-01-09.html">Next post</a></li> - </ul> - </div> - <div id="content"> - <h2 id="titleh" class="TText" style="font-wight:normal;">2-in-1</h2> - <div id="datetags" class="TText" style="margin-bottom:1em;">2016-09-24<br>#devel #qmidiplayer #c++ #qt</div> - <hr><div id="article" class="TText"> -<article> -<p> -The visualization plugin for QMidiPlayer in Linux has suffered from a dbus-related bug for a long time: -after you have opened the visualization window, close it and try to bring it up again, it will either -result in several lines of dbus warning which suggests there's a bug in the program (on Debian sid), -or simply a crash (on Arch Linux). -</p> -<p> -Well, I have to admit the design of QMidiPlayer's visualization architecture is pretty weird: -the visualization plugin spawns its own thread and do almost everything in it. After doing some -research on the Internet, I realized that everyone suggests that Qt and SDL <i>shouldn't</i> be -used together, "use QtOpenGL instead". However I thought that will hang the main UI thread and -I just don't believe in the myth. -</p> -<p> -So I started my investigation in early May. I even opened an related issue on github. Unfortunately nobody -offered help. So I had to solve the issue myself. First I had a look into the dbus warnings: -</p><pre style="white-space: pre-wrap;">process <PID>: arguments to dbus_connection_unref() were incorrect, assertion "connection->generation == _dbus_current_generation" failed in file ../../dbus/dbus-connection.c line 2822. -This is normally a bug in some application using the D-Bus library. -</pre> -<p></p> -<p> -Qt definitely uses dbus. After spitting these into stderr, QMidiPlayer crashes instantly in the -QDBusConnection thread. Googling the warning turned out nothing. Then I came across with this blog post -from a KDE developer:<br> -<a href="https://blogs.kde.org/2009/03/26/how-crash-almost-every-qtkde-application-and-how-fix-it-0">https://blogs.kde.org/2009/03/26/how-crash-almost-every-qtkde-application-and-how-fix-it-0</a> -</p> -<p> -Unfortunately, after applying the "fix", the bug didn't change even a little bit. So I had to move on. -</p> -<h3 id="tocanch0" class="tvis">UPD 2016-10-28</h3> -<p> -After several months' idleness of the investigation due to the lack of idea, I suddenly decided to have -a look at all dbus calls when QMidiPlayer crashes. Then I found the following dbus call: -</p><pre style="white-space: pre-wrap;">path=/org/freedesktop/ScreenSaver; interface=org.freedesktop.ScreenSaver; method=Inhibit; -string "My SDL application" -string "Playing a game" -</pre> -<p></p> -<p> -Apparently SDL is also using dbus to do some dirty work -- disabling the screen saver! So I appended -SDL_EnableScreenSaver in SMELT's init function. Unfortunately, nothing happened again. However I've -guessed out the cause to the problem: <b>both Qt and SDL try to initialize a dbus connection in <i>one</i> -process, which is not allowed. So I have to get rid of either one of them.</b> -</p> -<p> -Therefore I began to port the SMELT engine to GLFW. After two days of work, the port was finished and it worked -like a charm -- I have solved the problem! -</p> -<h4 id="tocanch1" class="tvis">BUT THAT'S NOT THE END OF THE STORY.</h4> -<p> -Driven by the unstoppable merriness after fixing a long-existed bug, I started to build GLFW version of -SMELT for Windows. The process was painful but finally I managed to do it successfully. After that -it's time to compile the visualization library. A beautiful DLL file, sized 1096192 bytes, was produced. -This build is almost 4x smaller than the previous failed mingw build and I regarded this as a omen of -fortune. -</p> -<p> -I put the DLL file into the plugin folder of QMidiPlayer and launched the application. No errors occured -as the mingw build once caused and the plugin showed up correctly in the plugin manager. I was so excited -that I turned on the plugin immediately and I couldn't wait to announce the result to my friends. However -when I hit the visualization I was greeted by a déjà vu scene. -</p> -<img src="//filestorage.chrisoft.org/blog/img/qmpcrash.png" alt="" width="70%" decoding="async"> -<p> -And this nasty little dialog from the Windows 2000 era. -</p> -<img src="//filestorage.chrisoft.org/blog/img/couldntbewritten.png" alt="" width="40%" decoding="async"> -<p> -So another tale of a battle between a fierce bug and me is due to happen. <s>Stay tuned and watch the fight!</s> -</p> -<a id="n1" href="#note1" class="note">[1]</a> -<h3 id="tocanch2" class="tvis">UPD@2016-12-28</h3> -<p> -So the bug has been (mostly) fixed by the following two commits!<br> -<a href="https://github.com/chirs241097/QMidiPlayer/commit/b79c4b7e3cab3711e87ba9e28fa8423a84ea7efa">b79c4b7e3cab3711e87ba9e28fa8423a84ea7efa@QMidiPlayer</a><br> -<a href="https://github.com/BearKidsTeam/SMELT/commit/b13f72857af93489f535b84d62882f681dc84a73">b13f72857af93489f535b84d62882f681dc84a73@SMELT</a><br> -</p> -<p> -Basically the most tough part to debug is caused by the stupidest typo... -</p><pre style="padding-left:20px;border:1px white solid;">@@ -62,7 +62,7 @@ bool SMELT_IMPL::smInit() - else if(i==0x80000004) - memcpy(cpuName+32, CPUInfo, sizeof(CPUInfo)); - } - - while(*cpuName=' ')++cpuName; - + while(*cpuName==' ')++cpuName; - smLog("%s:" SLINE ": CPU: %s\n", SYS_SDL_SRCFN,cpuName); - free(loced); -</pre> -<p></p> -<p> -This naïve mistake screwed up the memory and this should be the cause that made the debugger report different stack traces in different build modes... -(that reminds me of the experience of screwing up the call stack, in which the backtrace was filled up by "0x0000000000000000 in ??()"...) -</p> -<p> -After having fixed this, it was much easier to debug the application. Soon afterwards the first working visualization plugin for QMP on Windows -came out. -</p> -<p> -Finally I have to make more complaints about the develop environment for a cross-platform C++ application developer in Microsoft Windows. -It's bloated, complicated and confusing. I wonder whether Microsoft is deliberately making it difficult in order to force more developers -to migrate to C#/.Net. What a big ambition Microsoft is bearing! -</p> -<article> -</article></article></div><br><hr> - <div class="TText" id="notediv" style="font-size:80%;"><span class="TText"><a id="note1" href="#n1">[1]</a>: - Current status of the bug in Windows:<br> - Release build QMidiPlayer+Release build plugin=crash at somewhere in visualization.dll.<br> - Release build QMidiPlayer+Debug build plugin=crash at somewhere in Qt5Core.dll.<br> - Debug build QMidiPlayer+Debug build plugin=crash instantly on launch at plugin initialization.<br> -I have totally no idea about what to do next. -<br></span></div> - <div id="insanch" style="height:3em;"></div> - <div id="footer" style=""> - <div id="pagesw" class="TText" style="width:100%;height:0.5em;"></div> - <div style="text-align:center;" class="TText"> - Proudly powered by SSBS <reduced style="font-size:70%;">(the static stupid blogging system)</reduced> 2.5 - <br> - Content licensed under CC BY-SA 4.0. <span id="purgep" style="display:none;font-size:70%;">This page has passphrase(s) stored. 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