GUI application hangs (forever) if heavy thread starts in parallel
lazarus / 31-LCL

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Dmitry24 · 2016-07-02 11:37

Unfortunately I encountered a strange problem when heavy thread is
started programmatically at startup in parallel to main application.
Application window sometimes stops responding at all (even button is
not drawn). The only solution found is to start thread on timer and
with the timer interval large enough. However it seems unreliable
solution. The later thread starts the rarer the problem happen (but no
guarantee it disappears at all for a certain interval). In most of
examples threads are usually started on button clicks that is some
time after form creation so that examples are not affected.

The problems never happens while debugging.
If the thread gives timeslices (e.g. threadswitch or even there is no
heavy loop) there is no problem.

Below is the example application where several points were tried to
start the thread. The only workaround for me is to start inside the
timer with interval of 200 ms (20 ms is not enough) or to start
manually with button or to use threadswitch inside the thread for time
slices. Otherwise window may hangs (however not always).

Please give any advice...
Lazarus 1.6 64-bit compiled in DEBUG mode and run on Ubuntu 14

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils,
FileUtil, Forms, Controls, Graphics, Dialogs,  StdCtrls,
ExtCtrls; type   { TForm1 }   TForm1 = class(TForm)    Button1:
TButton;    Timer1: TTimer;    procedure Button1Click(Sender:
TObject);    procedure FormCreate(Sender: TObject);    procedure
Idle(Sender: TObject; var Done: boolean);    procedure
Timer1Timer(Sender: TObject);  private    threadcreated: boolean;    {
private declarations }  public    { public declarations }  end; var 
Form1: TForm1; implementation {$R *.lfm} const  appTerminate: boolean
= false; type    TThread1 = class(TThread)    protected      procedure
Execute; override;    public      Constructor Create(CreateSuspended :
boolean);    end;   constructor TThread1.Create(CreateSuspended :
boolean);  begin    FreeOnTerminate := True;    inherited
Create(CreateSuspended);  end;   procedure TThread1.Execute;  var   
i, j: integer;  begin    j:=0;    for i:=0 to 200000000 do begin     
j:=j+1;      //if (j and $FFFF=0) then threadswitch;    end;   
appTerminate:=true;  end; { TForm1 } procedure
TForm1.Button1Click(Sender: TObject);begin 
//TThread1.Create(false);end; procedure TForm1.Idle(Sender: TObject;
var Done: boolean);begin  if (appTerminate) then begin   
Application.Terminate;    exit;  end;   Done:=true;   if
(threadcreated) then exit;  //threadcreated:=true;
TThread1.Create(false);end; procedure TForm1.Timer1Timer(Sender:
TObject);begin  if (threadcreated) then exit;  //threadcreated:=true;
TThread1.Create(false);end; procedure TForm1.FormCreate(Sender:
TObject);begin  threadcreated:=false;  Application.OnIdle:={$IFDEF
FPC}@{$ENDIF}Idle;  threadcreated:=true;
TThread1.Create(false);end; end.  program project1; {$mode
objfpc}{$H+} uses  {$IFDEF UNIX}  cthreads, cmem,  {$ENDIF} 
Interfaces, // this includes the LCL widgetset  Forms, Unit1  { you
can add units after this }; {$R *.res} begin 
RequireDerivedFormResource:=True;  Application.Initialize; 
Application.CreateForm(TForm1, Form1);  Application.Run;end.   
Finally, it is found that even the following app freezes sometimes
when run not from IDE (for those who does not read the rest).

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i     program
project1;         {$mode objfpc}{$H+}         uses      Interfaces, //
this includes the LCL widgetset      Forms;         {$R *.res}       
var      Form1: TForm;    begin      Application.Initialize;     
Application.CreateForm(TForm, Form1);      Application.Run;    end.

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rvk · 2016-07-04 14:05

I can't reproduce this in virtualbox with Ubuntu 16 with the given
source.

I do have a small note about the {$IFDEF FPC}@{$ENDIF} use.
If you use {$MODE DELPHI} this will not work correctly (@ shouldn't be
used while FPC is still defined).

You could use
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Application.OnIdle:={$IFNDEF FPC_DELPHI}@{$ENDIF}Idle; or if the
source also needs to be compiled in Delphi:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Application.OnIdle:={$IFDEF FPC}{$IFNDEF
FPC_DELPHI}@{$ENDIF}{$ENDIF}Idle;

----------------------------------------------------------------------
Dmitry24 · 2016-07-04 15:23

Thank you for responding. Thank you for the note. {$mode objfpc}
directive is on the second line. Idle may be simply removed.

Sometimes app freezes on startup (empty not responding window appears,
sometimes buttons is drawn but also not responding). The second thread
always completes successfully. If the second thread interacts with the
main thread it also freezes. Even with 200 ms delay it sometimes
freezes, and almost always without a delay, in release mode too. The
same on Ubuntu 16 in Vmware.

Additionally I found it freezes rarely when run from GUI file panel
(Files) and almost always freezes when run from terminal. Additionally
it seems never freezing when I run using sudo.

It seems there is no problem with 32-bit compiled app, only with
64-bit.
Could you sent the compiled app to make sure it is not a wrong
compilation? How to attach a big file?

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rvk · 2016-07-04 16:15

Quote from: Dmitry24 on July 04, 2016, 05:23:45 pmThank you for the
note. {$mode objfpc} directive is on the second line. Idle may be
simply removed.In case you use objfpc you could have omitted the
{$IFDEF FPC} completely. Normally this is done for using same source
in Delphi. But if used in FPC you could have mode Delphi at the top in
which case the IFDEFs I gave were more appropriate. (but indeed, for
this test-case they are not necessary).

QuoteAdditionally I found it freezes rarely when run from GUI file
panel (Files) and almost always freezes when run from terminal.
Additionally it seems never freezing when I run using sudo.Yes, I have
it now too. It always works in the IDE. But I have it just the other
way around. It seems to ALWAYS work if I run from terminal. But
sometimes freezes (after 3 or 4 tries) when run from the file-
explorer 

You can't attach binaries here on the site (only small zip-files for
sourcecode).
Attached is my test-project and a temporary dropbox-link to the
project1 executable:
https://www.dropbox.com/s/4fhyrmujuki9qlc/project1.zip?dl=0

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rvk · 2016-07-04 16:26

Additionally the problem might be in the way you terminate the
program.

Have you tried a loop of 800000000.
When I do that it always works. The program has sufficient time to
complete the creation of the Form1. When you have a small loop the
thread is ending really soon and if the form isn't drawn yet (because
of the busy thread) you terminate the program too soon.

Does increasing the loop work for you?
If that doesn't work... what happens if you just comment out the
Application.Terminate ?

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Dmitry24 · 2016-07-04 17:00

Historically I write for FPC mode objfpc and for Delphi so there are
such defines.

Quote from: rvk on July 04, 2016, 06:15:57 pmYes, I have it now too.
It always works in the IDE. Yes, I wrote the problems never happens
while debugging. I mean in IDE it never happens.
QuoteBut I have it just the other way around. It seems to ALWAYS work
if I run from terminal. But sometimes freezes (after 3 or 4 tries)
when run from the file-explorer 
Sometimes it works from terminal many times in a row for me.
QuoteYou can't attach binaries here on the site (only small zip-files
for sourcecode).
Thant you, it seems it is not necessary since the problem reproduced.
QuoteAdditionally the problem might be in the way you terminate the
program.
I tried without auto terminating at all (it was just for simplicity of
testing). It freezes anyway. Example is below

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils,
FileUtil, Forms, Controls, Graphics, Dialogs,  StdCtrls,
ExtCtrls; type   { TForm1 }   TForm1 = class(TForm)    Button1:
TButton;    procedure Button1Click(Sender: TObject);    procedure
FormCreate(Sender: TObject);  private    { private declarations } 
public    { public declarations }  end; var  Form1:
TForm1; implementation {$R *.lfm} type    TThread1 = class(TThread)  
protected      procedure Execute; override;    public      Constructor
Create(CreateSuspended : boolean);    end;   constructor
TThread1.Create(CreateSuspended : boolean);  begin    FreeOnTerminate
:= True;    inherited Create(CreateSuspended);  end;   procedure
TThread1.Execute;  var    i, j: integer;  begin    j:=0;    for i:=0
to 200000000 do begin      j:=j+1;      //if (j and $FFFF=0) then
threadswitch; <- giving time slices helps    end;  end; { TForm1
} procedure TForm1.Button1Click(Sender: TObject);begin 
TThread1.Create(false);end; procedure TForm1.FormCreate(Sender:
TObject);begin  TThread1.Create(false);end; end. 
Increasing loop does not help me (just checked again). Are you sure it
really always helps you? Main thread freezes during the loop in the
second thread. I spent two days searching bug in my big multithreaded
application... And finally reduced it to an example above  I need to
make some startup quite heavy calculations just after the form is
created.

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rvk · 2016-07-04 18:43

Quote from: Dmitry24 on July 04, 2016, 07:00:30 pmSometimes it works
from terminal many times in a row for me.
Ok, finally after doing 25 times ./project1, enter, alt_f4, up, enter,
alt_f4, up, enter, alt_f4 I finally had it hang on terminal too. But
via the file-explorer it usually hangs the 1st through 4th time.

I've tried some things (dummy thread-initialization,
CheckSynchronize()) but couldn't pin down why this would happen. But
this goes beyond my ability to debug.

Even removing FreeOnTerminate and doing this makes it hang:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender: TObject);var  t :TThread1;begin  t :=
TThread1.Create(false);  t.WaitFor;  t.Free;end;In that case your
thread is already ended when the form resumes creating.
It still hangs with a blank form.
(So I'm wondering if it's really your "busy" thread that's at fault or
something else.

Even this makes it hang after enough times (so without running a
thread):
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender: TObject);var  t :TThread1;begin  //t :=
TThread1.Create(false);  //t.WaitFor;  //t.Free;end;So it might be
just a general problem which the thread makes worse.

Edit: Even starting a form with one button without the cthreads in the
uses of the project, the project hangs after about 25 starts from the
file-explorer.

Edit #2: Now even after 1 or 2 starts. Seems like 64bit Lazarus is
really unstable.

Simple example of a button starting the same executable and exiting.
Press the button a few times and see it hang.
(How does it work for you?)

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils,
FileUtil, Forms, Controls, Graphics, Dialogs,  StdCtrls,
ExtCtrls; type   { TForm1 }   TForm1 = class(TForm)    Button1:
TButton;    procedure Button1Click(Sender: TObject);    procedure
FormCreate(Sender: TObject);  private    { private declarations } 
public    { public declarations }  end; var  Form1:
TForm1; implementationuses Process; {$R *.lfm} { TForm1 } procedure
TForm1.Button1Click(Sender: TObject);var  AProcess: TProcess;begin 
AProcess := TProcess.Create(nil);  AProcess.Executable:= ParamStr(0); 
AProcess.Execute;  AProcess.Free;  Close;end; procedure
TForm1.FormCreate(Sender: TObject);beginend; end.

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Dmitry24 · 2016-07-05 05:54

Yes, a few times with TProcess (more often from File Explorer).
Finally, I removed everything and still was able to get freeze several
times for the app:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
project1; {$mode objfpc}{$H+} uses  Interfaces, // this includes the
LCL widgetset  Forms; {$R *.res} var  Form1: TForm;begin 
Application.Initialize;  Application.CreateForm(TForm, Form1); 
Application.Run;end. 
I don't know if all Uses are necessary for freeze because I had
success (freeze) only two times for this app. Now I can't get freezing
any more for such simple app regardless the number of retries. It
seems some delay at startup may cause the freeze. A heavy thread or
other circumstances may give such a delay.

Currently I continue testing and can't get freeze anymore for anyone
of apps... So sometimes the problem may dissappear at all on a system
and is not reproducible 

After reloading the system the problem appears again even for the
simplest app. I removed unnecessary Uses (updated the example) and
still sometimes it freezes.

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User137 · 2016-07-05 07:35

Making a few changes in code, marked with comments (not testing, not
sure if helps):
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils,
FileUtil, Forms, Controls, Graphics, Dialogs,  StdCtrls,
ExtCtrls; type   { TForm1 }   TForm1 = class(TForm)    Button1:
TButton;    Timer1: TTimer;    procedure Button1Click(Sender:
TObject);    procedure FormCreate(Sender: TObject);    procedure
Idle(Sender: TObject; var Done: boolean);    procedure
Timer1Timer(Sender: TObject);  private    threadcreated: boolean;    {
private declarations }  public    { public declarations }  end; var 
Form1: TForm1; implementation {$R *.lfm} const  appTerminate: boolean
= false; type    TThread1 = class(TThread)    protected      procedure
Execute; override;    public      Constructor Create(CreateSuspended :
boolean);    end;   constructor TThread1.Create(CreateSuspended :
boolean);  begin    inherited Create(CreateSuspended); // Normally
inherit parent constructor first    FreeOnTerminate := True;   
//inherited Create(CreateSuspended);  end;   procedure
TThread1.Execute;  var    i, j: integer;  begin    j:=0;    //for i:=0
to 200000000 do begin    for i:=0 to 200 do begin // Test with smaller
value first, does it freeze?      j:=j+1;      //if (j and $FFFF=0)
then threadswitch;    end;    appTerminate:=true;  end; { TForm1
} procedure TForm1.Button1Click(Sender: TObject);begin 
//TThread1.Create(false);end; procedure TForm1.Idle(Sender: TObject;
var Done: boolean);begin  Done:=true; // Set first, otherwise it will
remain false when it terminates  if (appTerminate) then begin   
appTerminate:=false; // Just making sure it won't do this again, it's
idle event afterall, who knows how often it's called   
Application.Terminate;    exit;  end;   //Done:=true;   if
(threadcreated) then exit;  //threadcreated:=true;
TThread1.Create(false);end; procedure TForm1.Timer1Timer(Sender:
TObject);begin  if (threadcreated) then exit;  //threadcreated:=true;
TThread1.Create(false);end; procedure TForm1.FormCreate(Sender:
TObject);begin  threadcreated:=false;  Application.OnIdle:={$IFDEF
FPC}@{$ENDIF}Idle;  threadcreated:=true;
TThread1.Create(false);end; end.  program project1; {$mode
objfpc}{$H+} uses  {$IFDEF UNIX}  cthreads, cmem,  {$ENDIF} 
Interfaces, // this includes the LCL widgetset  Forms, Unit1  { you
can add units after this }; {$R *.res} begin 
RequireDerivedFormResource:=True;  Application.Initialize; 
Application.CreateForm(TForm1, Form1);  Application.Run;end.

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Dmitry24 · 2016-07-05 08:41

Please, read the previous message just before your answer... What
changes could you suggest to the code above?

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rvk · 2016-07-05 13:01

I tried the original (with thread) on Mint and it worked fine (no
hangs).
Reinstalled Ubuntu and Lazarus (with fpclazup) and again... after a
few starts it hangs.

Not sure if that's because Ubuntu is way heavier than Mint, and
consequently uses more resources which makes it hang, but either
way... it shouldn't happen.

I wouldn't be comfortable with releasing a 64bit version of software
which "might" hang unexpectedly.

Edit: yep. even an empty project with one button will hang if started
repeatedly (sometimes after 4 or 5 tries, sometimes after much much
more, like 50 tries but it eventually hangs).

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Cyrax · 2016-07-05 16:02

Can you guys check if Lazarus trunk and FPC trunk have same problem?
Please disable any optimization options, too.

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rvk · 2016-07-05 19:41

O, I thought I tried trunk first but apparently that was for something
else.

After some trouble with fpclazup I managed to install trunk.
First, with startlazarus, lazarus hanged a few times on the splash
screen but finally I got it going.

But unfortunately, trunk had the same result. The simple
TProcess/run_by_button example hangs after about 8 runs.

What did you mean by "disable any optimization options"?
In FPC/Lazarus during compile or in Ubuntu (VM)?

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Cyrax · 2016-07-06 00:30

By disabling any optimization settings I mean compiling FPC, Lazarus
and test program with "-O-"  option.

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fpcoder · 2016-07-06 02:59

FWIW, with no changes I compiled rvk's thread.zip project with Laz
trunk and release fpc 3.0 under Ubuntu 16.04 - 64 bits. The
application always starts and finishes, no matter if it starts from
terminal, filemanager or Run from Lazarus.

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Dmitry24 · 2017-02-16 06:38

Still have the same issue with Lazarus 1.6.2 
[The simplest 64-bit Linux app hangs at startup from time to time]

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balazsszekely · 2017-02-17 05:44

Did you try to create the thread suspended and let the GUI finish
initializing. Start/resume the thread after that,  use a timer or
another mechanism to achieve this.

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Dmitry24 · 2017-02-17 06:13

With periodical thread switching (if uncomment threadswitch line) it
almost never hangs. Actually even the default blank application may
hang (as was written above) but very very rarely. With heavy thread
the effect is almost always when run the app from command line [now
using Ubuntu 16.0 x64 on Vmware].

I attached to the frozen app and got stack traces. Maybe this may help
somehow.

Thread 1
Quote#0 syscall at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1 ?? at :0
#2 g_dbus_connection_send_message_with_reply at :0
#3 ?? at :0
#4 g_dbus_connection_call at :0
#5 ?? at :0
#6 ?? at :0
#7 g_initable_new_valist at :0
#8 g_initable_new at :0
#9 gvfs_dbus_mount_tracker_proxy_new_for_bus_sync at :0
#10 ?? at :0
#11 ?? at :0
#12 g_type_create_instance at :0
#13 ?? at :0
#14 g_object_newv at :0
#15 g_object_new at :0
#16 ?? at :0
#17 ?? at :0
#18 g_file_new_for_path at :0
#19 ?? at :0
#20 g_type_create_instance at :0
#21 ?? at :0
#22 ?? at :0
#23 ?? at :0
#24 g_object_new_valist at :0
#25 g_object_new at :0
#26 ibus_bus_new_async at :0
#27 ?? at :0
#28 g_type_class_ref at :0
#29 g_object_newv at :0
#30 g_object_new at :0
#31 ibus_im_context_new at :0
#32 ?? at :0
#33 ?? at :0
#34 ?? at :0
#35 RESETDEFAULTIMCONTEXT at gtk2/gtk2globals.pp:422
#36 GTKFOCUSCB(0x172e360, 0x177f6e0, 0x17deef8) at
gtk2/gtk2callback.inc:1038
#37 GTK2FOCUSCB(0x172e360, 0x177f6e0, 0x17dbfb8) at
gtk2/gtk2widgetset.inc:54
#38 ?? at :0
#39 g_closure_invoke at :0
#40 ?? at :0
#41 g_signal_emit_valist at :0
#42 g_signal_emit at :0
#43 ?? at :0
#44 gtk_main_do_event at :0
#45 ?? at :0
#46 g_main_context_dispatch at :0
#47 ?? at :0
#48 g_main_context_iteration at :0
#49 gtk_main_iteration_do at :0
#50 APPPROCESSMESSAGES(0x16b05a8) at gtk2/gtk2widgetset.inc:2318
#51 HANDLEMESSAGE(0x16ae378) at include/application.inc:1262
#52 RUNLOOP(0x16ae378) at include/application.inc:1399
#53 APPRUN(0x16b05a8, {Proc = {procedure (POINTER)} 0x7ffd4333b350,
Self = 0x16ae378}) at include/interfacebase.inc:54
#54 RUN(0x16ae378) at include/application.inc:1387
#55 main at project1.lpr:19

Thread 2
Quote#0 poll at ../sysdeps/unix/syscall-template.S:84
#1 ?? at :0
#2 g_main_context_iteration at :0
#3 ?? at :0
#4 ?? at :0
#5 start_thread(0x7f63c9058700) at pthread_create.c:333
#6 clone at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 3
Quote#0 poll at ../sysdeps/unix/syscall-template.S:84
#1 ?? at :0
#2 g_main_context_iteration at :0
#3 ?? at :0
#4 ?? at :0
#5 start_thread(0x7f63c8857700) at pthread_create.c:333
#6 clone at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 4
Quote#0 __lll_lock_wait at
../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1 __GI___pthread_mutex_lock(0x16c7f90) at
../nptl/pthread_mutex_lock.c:115
#2 g_type_class_ref at :0
#3 g_object_newv at :0
#4 g_object_new at :0
#5 ?? at :0
#6 ?? at :0
#7 ?? at :0
#8 ?? at :0
#9 ?? at :0
#10 ?? at :0
#11 ?? at :0
#12 g_main_context_dispatch at :0
#13 ?? at :0
#14 g_main_loop_run at :0
#15 ?? at :0
#16 ?? at :0
#17 start_thread(0x7f63c3fff700) at pthread_create.c:333
#18 clone at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

For thread 1 there may be different functions between #0 syscall and
g_type_create_instance at :0 but others are the same between runs.

----------------------------------------------------------------------
AlexVas · 2017-06-14 02:35

Hi,

I have the same issue running Ubuntu 16.04.2 LTS in a VirtualBox on
iMac Retina 2016.

It hangs reliably. Our testers reported the issue too.

Just wondering if there are any known workarounds? I am stuck.

Thank you.