Threading OSX and DYLIBs
lazarus / 33-macOS - Mac OS X

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kevin.black · 2019-06-13 03:28

MBP with parallels Mojave VM lazarus 2.0.0RC3

I have read the tutorial docs WRT threading and it appears quite
straight forward. I say that noting that so far, everything I have
tried on OSX either hasn't worked or required some not so obvious
surgery to get it to work. Threading under windows seems to work fine,
on OSX not so much. Again, I have pursued the forum and wiki and not
getting much out of it. Here are my code snippets, most of which is
straight out of the tutorial:

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 {$mode
objfpc}{$H+}{$ModeSwitch pChartoString}{$define
UseCThreads} interface uses  {$IFDEF UNIX}  {$IFDEF UseCThreads} 
cthreads,  {$ENDIF}  {$ENDIF}  Interfaces,......const  {$IFDEF
MSWINDOWS}  EmpyreanAPIDLL = 'DbXServerAPI.dll';  libEmpyreanCrypto =
'libEmpyreanCrypto.dll';  {$ENDIF MSWINDOWS}  {$IFDEF DARWIN} 
EmpyreanAPIDLL = 'libdbxserverapi.dylib';  {$linklib
libdbxserverapi.dylib}  libEmpyreanCrypto =
'libEmpyreanCrypto.dylib';  {$linklib libEmpyreanCrypto.dylib} 
{$ENDIF DARWIN}......type  TgetStatusThread = class(TThread)  private 
  fStatusText: string;    eMail: string;    procedure ShowStatus; 
protected    procedure Execute; override;  public   Constructor
Create(CreateSuspended : boolean);end;......function
checkUserStatus(loginName: pChar; out successBoolean: pChar;  out
responseMessage: pChar; out errorCode: pChar; out errorMessage: pChar)
 : integer;  {$IFDEF MSWINDOWS}stdcall;{$ELSE}cdecl;{$ENDIF} external
EmpyreanAPIDLL;...... constructor
TgetStatusThread.Create(CreateSuspended : boolean);begin  inherited
Create(CreateSuspended);  FreeOnTerminate := True;end;......procedure
TfEMPServerTest.bCheckUserStatusClick(Sender: TObject);var 
getStatusThread: TgetStatusThread; begin  WriteLog('DEBUG', 'in
TfEMPServerTest.bCheckUserStatusClick');  getStatusThread :=
TgetStatusThread.Create(True);  WriteLog('DEBUG', 'before start'); 
getStatusThread.Email := checkUserStatusEmailEdit.Text; 
getStatusThread.Start;     // START THE THREAD - YES THIS WORKS 
WriteLog('DEBUG', 'after start'); end; procedure
TgetStatusThread.ShowStatus;// this method is executed by the
mainthread and can therefore access all GUI elements.begin 
fEMPServerTest.Memo1.Lines.Add('Status Returned: ' + fStatusText); 
showmessage('TgetStatusThread.ShowStatus Status Returned: ' +
fStatusText);  WriteLog('DEBUG', 'Status Returned: ' +
fStatusText);end; procedure TgetStatusThread.Execute;var 
successBoolean: pChar;  responseMessage: pChar;  errorCode: pChar; 
errorMessage: pChar;  ReturnResult: integer;  newStatus :
string; begin  Writelog('DEBUG', 'In TgetStatusThread.Execute
Thread');   // I DEFINATELY GET HERE AND THE LOG IS WRITTEN TO 
fStatusText := 'TgetStatusThread Starting...';  Writelog('DEBUG',
fStatusText);  Synchronize(@Showstatus);  fStatusText :=
'TgetStatusThread Running...';  Writelog('DEBUG', fStatusText); 
Synchronize(@Showstatus);  responseMessage := 'Nil Response'; 
ReturnResult := checkUserStatus(pChar(Email), successBoolean,
responseMessage, errorCode, errorMessage);  // THIS IS A CALL TO A
FUNCTION IN A DYLIB AND IT HANGS HERE  WriteLog('DEBUG',
'TgetStatusThread.Execute after checkUserStatus');                   
                  // NEVER EXECUTED  fStatusText := 'Return Result: '
+ inttostr(ReturnResult) + #13#10 + 'Response: ' +
string(responseMessage);  Synchronize(@Showstatus);  fStatusText :=
'TgetStatusThread Terminating...';  Synchronize(@Showstatus); 
WriteLog('DEBUG', fStatusText);   while (not Terminated) and
(responseMessage = 'Nil Response')do  begin    NewStatus :=
'TgetStatusThread Update';    Writelog('DEBUG', NewStatus);    if
NewStatus <> fStatusText then    begin      fStatusText := newStatus; 
    Writelog('DEBUG', 'TgetStatusThread Loop synchronize');     
Synchronize(@Showstatus);    end;  end; end; 
Problem #1:
So the first issue is that Synchronize never executes the ShowStatus
method (hence the gazillion Writelog statements so I can see what's
happening).

Is this some issue with OSX or is it something else more insidious?

Problem #2:
When I get to the external function (which works fine if I just call
it from the main thread), the code simply hangs. To complicate
matters, I am trying to have this DYLIB and it's functions used by a
C++ developer on macOS. If he calls from the main thread then OK, if
he calls the DYLIB function from a secondary thread it crashes his
application.

But first things first, does the DYLIB function need anything special
to be called from a secondary thread, and what is a likely reason it
is causing the call to hang?

If you need any other/further info let me know.

Would I have any better success with one of the other lazarus thread
libraries like say WThread?

Thanks,
Kevin

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skalogryz · 2019-06-13 13:21

1)
for this particular issue I can definitely recommend to try using
Lazarus trunk.
There were a number of changes done on how Synchronize() work.

2)
The crashes from the secondary thread depend on how the function is
written.
Typically a pure function like Min() or Max() would work fine.
BUT if a function is using some global objects, then it might crash
pretty fast.

A special consideration for macOS. It might require a special
NSAutorelease object to be created on the thread. However, those could
be created by the later OSX versions

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kevin.black · 2019-06-13 22:51

@skalogryz,

1. Thank you. I have installed FPC fixes 3.2.0 and lazarus 2.1.0. I'll
junk that and try and install fixes 3.2.0 and lazarus trunk.

2. The function within the DYLIB calls a couple of internal functions
(mainly writing to the log) and performs a REST call using some of the
TMS Dropbox component classes, the returned JSON is then decoded in
another function. In Delphi/Win32 I have used these classes within a
DLL called by a thread and there has been no issues that I am aware
of. The only other function is one to allocate memory etc to the pChar
values returned.  There are, AFAICT, no globals etc etc, but I cannot
confirm that in the TMS code.

Regardless, first thing to try is the install of Fixes/trunk. Thanks
for the advice.

Cheers,
Kevin

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kevin.black · 2019-06-14 02:35

So on the basis that it never rains it pours:
I have installed FPC 3.2/Lazarus TrunkWhen I try to build the test
application it can no longer find any of the DYLIBSAll of the library
paths are the same (it drags this in with the lpr file for each
project)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 const 
{$IFDEF MSWINDOWS}  EmpyreanAPIDLL = 'DbXServerAPI.dll'; 
libEmpyreanCrypto = 'libEmpyreanCrypto.dll';  {$ENDIF MSWINDOWS} 
{$IFDEF DARWIN}   EmpyreanAPIDLL = 'libdbxserverapi.dylib';  {$linklib
libdbxserverapi.dylib}  libEmpyreanCrypto =
'libEmpyreanCrypto.dylib';  {$linklib libEmpyreanCrypto.dylib}and
these lines are causing the linker error that the libraries are not
found (to be safe, I have put the DYLIBs in the app folder, in the app
itself, in a library folder and in /usr/local/lib, yet all I get is
this library not found error trying to build):

QuoteMessages, Warnings: 17, Hints: 78
...
...
Error: ld: library not found for -ldbxserverapi
An error occurred while linking
Error: Error while linking

So I cannot even tryout the 'fixes' in lazarus trunk until I can sort
out the libraries not found (which TBF is seeming a little daunting, I
cannot imagine where the linker is looking and why it isn't looking at
the folders where the DYLIBs are).

Does anyone know why the DYLIBs are not being found in this frehs
install?

Thanks,
Kevin