The basic commands for using apitrace with an OpenGL application are:
apitrace trace --api=gl MyApp qapitrace MyApp.trace apitrace dump --blobs MyApp.trace
The last command generates blobs that can be inspected with the following command, for example:
tail -c $((12*10)) ~/repos/MyApp/build/blob_call2325.bin | xxd -g1
Or by writing a simple C++ program that converts them into CVS format:
First we need to install certbot utility:
apt-get install software-properties-common
add-apt-repository ppa:certbot/certbot
apt-get update
apt-get install python-certbot-nginx
After that, we can easily generate SSL certificates for all the domains listed in Nginx ‘server_name’ attributes in alive (working) virtual hosts. The examples are:
sudo certbot --nginx certonly --cert-name slogpost.ru -d slogpost.ru -d www.slogpost.ru
sudo certbot certonly --nginx --cert-name sharlines.com -d sharlines.com -d www.sharlines.com
sudo certbot certonly --nginx --cert-name milomag.ru -d milomag.ru -d www.milomag.ru -d xn--80agwdbl3g.xn--p1ai -d www.xn--80agwdbl3g.xn--p1ai
sudo certbot certonly --nginx --cert-name developernote.com -d developernote.com -d www.developernote.com -d herb.developernote.com -d mastermag.developernote.com -d geographx.developernote.com -d git.developernote.com -d geographx.net -d www.geographx.net -d xn--80acc2atiigge7h.xn--p1ai -d www.xn--80acc2atiigge7h.xn--p1ai
(do not forget to run the commands above each time you add or remove a subdomain)
We cannot use wildcard domains line *.developernote.com with Let’s Encrypt, so we should list all the subdomains. And I do not see anything wrong in combining multiple domains in a single certificate.
To remove the certificate we do something like this:
certbot revoke --cert-path /etc/letsencrypt/live/developernote.com/fullchain.pem
certbot delete --cert-name developernote.com
Updating all the generated certificates:
certbot renew
After changing the website URL from HTTP to HTTPS, probably it makes a sense to update all the hyperlinks in MySQL database:
show tables;
show columns from wp_posts;
SELECT ID, post_title, post_date, post_name FROM wp_posts WHERE INSTR(post_content, 'http://slogpost.ru') <> 0;
UPDATE wp_posts SET post_content=REPLACE(post_content, 'http://slogpost.ru', 'https://slogpost.ru') WHERE INSTR(post_content, 'http://slogpost.ru') <> 0;
UPDATE wp_posts SET post_content=REPLACE(post_content, 'http://developernote.com', 'https://developernote.com') WHERE INSTR(post_content, 'http://developernote.com') <> 0;
The final step is adding certbot-renew.sh file to /etc/cron.monthly with the following content:
certbot renew
service squid reload
It seems like the service … command is completely ignored. Nothing in syslog, nothing in nginx logs. I switched to using
certbot renew
systemctl reload squid
instead, and this seems to work.
The following C++ code compares the performance of std::atomic and std::mutex:
#include <atomic>
#include <mutex>
#include <iostream>
#include <chrono>
#include <thread>
const size_t size = 100000000;
std::mutex mutex;
bool var = false;
typedef std::chrono::high_resolution_clock Clock;
void testA()
{
std::atomic<bool> sync(true);
const auto start_time = Clock::now();
for (size_t counter = 0; counter < size; counter++)
{
var = sync.load();
//sync.store(true);
//sync.exchange(true);
}
const auto end_time = Clock::now();
std::cout << 1e-6*std::chrono::duration_cast<std::chrono::microseconds>(end_time - start_time).count() << " s\n";
}
All the following commands assumes we saved MySQL root password into MROOTPASS variable:
export MROOTPASS=<mysql root password>
The most straight forward method to backup all the MySQL databases and all the website files (PHP scripts, images, etc..) stored in the /home directory is the following:
mysqldump --all-databases -u root -p$MROOTPASS | gzip > all-databases-$(date '+%Y-%m-%d_%H-%M-%S').sql.gz tar -cvzf home.tar.gz /home
If we backup some individual database (probably not as root) and change its user while restoring it, it might make a sense to remove DEFINER from the output script:
sed -e 's/*]*\*/\*/'
The following commands restore all the websites from the archives:
gunzip -c all-databases-2017-05-23_15-31-00.sql.gz | mysql -u root -p$MROOTPASS cd / sudo tar -xvzf home.tar.gz
After migration from MySQL version 14.14 Distrib 5.5.54 to 14.14 Distrib 5.7.18 (I do not know what is the difference between them) I got the following error: “ERROR 1805 (HY000) at line 1: Column count of mysql.user is wrong. Expected 45, found 42. The table is probably corrupted” while trying to drop some user, and fixed it by running:
mysql_upgrade -u root -p$MROOTPASS service mysql restart
The following bash script renames all the files matching src_name.* with dst_name.*:
src_name=$1 dst_name=$2 unset $1 cp $src_name.* ~/temp/ cd ~/temp/ rename "s/$src_name\.([a-z]+)/$dst_name\.\$1/" * cd - mv ~/temp/$dst_name.* .
If you have some files like src1.h and src1.cpp, you can save this script into dupsource.sh file, for example, and then rename those files with src2.h and src2.cpp using the following command:
dupsource.sh src1 src2
The script requires ~/temp directory to exist and be writable.
If QAudioDecoder does not decode mp3, reporting a format error (GStreamer; Unable to start decoding process), the following package can help:
On Ubuntu:
apt-get install gstreamer0.10-fluendo-mp3
On CentOS:
yum -y install http://li.nux.ro/download/nux/dextop/el7/x86_64/nux-dextop-release-0-5.el7.nux.noarch.rpm
yum install gstreamer{,1}-plugins-ugly
To learn OpenGL I wrote a simple game that utilizes the most of basic OpenGL ES 2.0 (and partially 3.0) techniques:
Install sox tool with mp3 support:
apt-get install sox apt-get install libsox-fmt-mp3 sox file.mp3 file.wav
Basically that is all, but if you need to check resulting wav file parameters like channels, sample rate, precision, duration, bit rate, etc…, use soxi command:
(more…)
First, I tried Valgrind tool using the following command:
valgrind --tool=memcheck --leak-check=yes ./app
With some large QT application started for some short period I got the following output:
==7090== HEAP SUMMARY:
==7090== in use at exit: 5,623,365 bytes in 36,268 blocks
==7090== total heap usage: 32,454,680 allocs, 32,418,412 frees, 12,822,939,874 bytes allocated
................................
==7090== LEAK SUMMARY:
==7090== definitely lost: 20,163 bytes in 74 blocks
==7090== indirectly lost: 60,053 bytes in 1,273 blocks
==7090== possibly lost: 396,167 bytes in 2,169 blocks
==7090== still reachable: 4,834,822 bytes in 31,576 blocks
==7090== suppressed: 0 bytes in 0 blocks
==7090== Reachable blocks (those to which a pointer was found) are not shown.
==7090== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==7090==
==7090== For counts of detected and suppressed errors, rerun with: -v
==7090== Use --track-origins=yes to see where uninitialised values come from
==7090== ERROR SUMMARY: 20905 errors from 1583 contexts (suppressed: 15 from 2)
When I left this app running for the night (approximately 16 hours), I got the following summary:
==3816== HEAP SUMMARY:
==3816== in use at exit: 7,746,701 bytes in 36,248 blocks
==3816== total heap usage: 827,800,342 allocs, 827,764,094 frees, 105,404,761,516 bytes allocated
..................................
==3816== LEAK SUMMARY:
==3816== definitely lost: 19,835 bytes in 38 blocks
==3816== indirectly lost: 59,805 bytes in 1,237 blocks
==3816== possibly lost: 396,167 bytes in 2,169 blocks
==3816== still reachable: 6,958,734 bytes in 31,628 blocks
==3816== suppressed: 0 bytes in 0 blocks
==3816== Reachable blocks (those to which a pointer was found) are not shown.
==3816== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==3816==
==3816== For counts of detected and suppressed errors, rerun with: -v
==3816== Use --track-origins=yes to see where uninitialised values come from
==3816== ERROR SUMMARY: 13022 errors from 1574 contexts (suppressed: 10 from 2)
It means that the app leaks about 0.126 MB/hour ( (6958734 – 4834822) / 16 / 1024.0 / 1024.0) and totally for the night 2.02 MB, and probably it is not a leak, because the app has pointers to the allocated memory (it is reachable), but it does not clean exit.
To figure out how it works I built the following trivial program:
int main()
{
int *a = new int[100];
}
with debug information and started the tool:
g++ -g -o ex ex.cpp
valgrind --tool=memcheck --leak-check=yes ./ex
In the output the tool shows line number 3 where memory leak is occurred:
==22042== Memcheck, a memory error detector
==22042== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==22042== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==22042== Command: ./ex
==22042==
==22042==
==22042== HEAP SUMMARY:
==22042== in use at exit: 73,104 bytes in 2 blocks
==22042== total heap usage: 2 allocs, 0 frees, 73,104 bytes allocated
==22042==
==22042== 400 bytes in 1 blocks are definitely lost in loss record 1 of 2
==22042== at 0x4C2B800: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==22042== by 0x40061B: main (ex.cpp:3)
==22042==
==22042== LEAK SUMMARY:
==22042== definitely lost: 400 bytes in 1 blocks
==22042== indirectly lost: 0 bytes in 0 blocks
==22042== possibly lost: 0 bytes in 0 blocks
==22042== still reachable: 72,704 bytes in 1 blocks
==22042== suppressed: 0 bytes in 0 blocks
==22042== Reachable blocks (those to which a pointer was found) are not shown.
==22042== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==22042==
==22042== For counts of detected and suppressed errors, rerun with: -v
==22042== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Links:
Another alternative is calling mallinfo() function in C++ code. The following code gets something like total heap size of the process:
int usedmem = mallinfo().uordblks;
Using this function I wrote a QT widget that shows memory usage in application status bar:
#include <QLabel>
#include <malloc.h>
class MemoryStatusWidget : public QLabel
{
public:
MemoryStatusWidget(QWidget *parent = nullptr);
public:
void timerEvent(QTimerEvent *) override;
};
MemoryStatusWidget::MemoryStatusWidget(QWidget* parent)
: QLabel(parent)
{
startTimer(1000);
}
void MemoryStatusWidget::timerEvent(QTimerEvent *)
{
int usedmem = mallinfo().uordblks;
setText(tr("Memory Usage:%1 MB").arg(QString::number((double)usedmem / (1024 * 1024), 'f', 3)));
}
Just in case if you need to detect leaks on Windows (where Valgrind doesn’t work and will never work by design), give Deleaker a try. By the way it can be integrated with Qt Creator, see video on YouTube.
Below I provided parameters of three Android phones I tested my Lines game with:
| Android Version | Screen Resolution | Pixel Ratio | DPI | Screen Size |
|---|---|---|---|---|
| 4.4? | 320×496 (480×744/706) | 1.5 | 156.89 | 52×80 mm |
| 4.4? | 360×592 (540×888/850) | 1.5 | 160.19 | 57×94 mm |
| 6.0 | 360×592 (720×1184/1136) | 2.0 | 160.19 | ~68×123 mm |
| N/A | 800×1232 | 1.0 | 188.3295 | 108×166 mm |
Screen Resolution column contains the information in the following format: <logical resolution> (<physical resolution>/<physical height available for applications in portrait orientation>.
DPIs with ‘~’ sign are measured manually because QT (or some Android API) provides incorrect Screen Size.
