Some threads does not execute after creating on Multi-threaded app - multithreading

Question

I've currently developing a program which executes some AT commands periodically.
I tried to make it multi-threaded because this program should work with 8 GSM modems concurrently.
here is my extended TThread class as TWorkerThread:
TWorkerThread = class(TThread)
private
FThreadJob : TThreadJobs;
FSimNum : Word;
FZylGSM : TZylGSM;
SL_AT : TStringList;
FSignalGauge : TsGauge;
procedure SyncProc;
public
TerminateThread : Boolean;
constructor Create;
property ThreadJob : TThreadJobs read FThreadJob write FThreadJob;
property ZylGSM : TZylGSM read FZylGSM write FZylGSM;
property SimNum : Word read FSimNum write FSimNum;
property SignalGauge: TsGauge read FSignalGauge write FSignalGauge;
protected
procedure Execute; override;
end;
And body of my thread's methods :
constructor TWorkerThread.Create;
begin
inherited Create(True);
if Not Assigned(SL_AT) then SL_AT := TStringList.Create;
SL_AT.Clear;
FThreadJob := tjNone;
TerminateThread := False;
FreeOnTerminate := True;
end;
procedure TWorkerThread.Execute;
begin
inherited;
if FThreadJob = tjNone then Exit;
while TerminateThread=False do Synchronize(SyncProc);
end;
procedure TWorkerThread.SyncProc;
var
ts : String;
SignalStrength : Byte;
begin
if bTerminateFlag then TerminateThread := True;
if TerminateThread then Exit;
case FThreadJob of
tjOperatorName : ;
tjSignalQuality :
begin
FZylGSM.ExecuteATCommand('AT+CSQ', SL_AT);
if (SL_AT.Count>2) And (Pos('OK', SL_AT[2])>0) then begin
ts := Copy(SL_AT[1], Pos(':', SL_AT[1])+1, Length(SL_AT[1]));
ts := Trim(ts);
if ts = '99' then ts:='0';
SignalStrength := StrToIntDef(ts, 0);
SignalGauge.Progress := SignalStrength;
end;
if bTerminateFlag then TerminateThread := True;
// Application.ProcessMessages;
end;
end;
end;
I've used a for loop to create 8 threads like this:
DevPorts.GSM_Ports[i].WorkerThread := TWorkerThread.Create;
DevPorts.GSM_Ports[i].WorkerThread.ThreadJob := tjSignalQuality;
DevPorts.GSM_Ports[i].WorkerThread.SimNum := i+1;
DevPorts.GSM_Ports[i].WorkerThread.SignalGauge := FindComponent('Sig_'+IntToStr(i)) as TsGauge;
DevPorts.GSM_Ports[i].WorkerThread.ZylGSM := DevPorts.GSM_Ports[i].Comm;
DevPorts.GSM_Ports[i].WorkerThread.Start;
The program worked as expected when I commented "Application.ProcessMessages", the problem is when I use "Application.ProcessMessages" in "TWorkerThread.SyncProc", some of my threads don't executes. I know it could be wrong to use ProcessMessage in the thread function but I did it because the Main GUI thread hangs up during send/recv of threads.
Any help will be appreciated.

Answer 1

Do not call Application.ProcessMessages from your threads. This is a terrible thing to do. The best you can hope for is spectacular failures. It calls code that should be run on the main thread on the wrong threads.
The reason your main GUI thread hangs is because you're not running anything multi-threaded. The line while TerminateThread=False do Synchronize(SyncProc); is synchronising everything to run back on the main thread. So currently your threads are pointless.
The purpose of Synchronize() is to allow threads to coordinate access to shared data so you don't have to deal with race conditions. However, the ideal is to share as little data as possible so that your threads can work independently of each other (and the main thread), without having to worry values under its control being changed at inappropriate times.
So alarm bells are screaming when you make most of your worker thread's members public:
public
TerminateThread : Boolean;
constructor Create;
property ThreadJob : TThreadJobs read FThreadJob write FThreadJob;
property ZylGSM : TZylGSM read FZylGSM write FZylGSM;
property SimNum : Word read FSimNum write FSimNum;
property SignalGauge: TsGauge read FSignalGauge write FSignalGauge;
You need to reevaluate what the responsibilities of your worker threads are and encapsulate that work appropriately. (Only call Synchronize() for code that should be synchronised!) However, I'm not familiar with the components you're using, and you may find that they're poorly written and not suitable for multi-threading as a result.
Other problems
Apart from the glaring immediate problems you have. There are also a number of mistakes demonstrating gaps in your understanding of multi-threaded development.
Do not call inherited from TWorkerThread.Execute. The ancestor method is abstract - has no implementation an cannot be called. And even though the Delphi compiler generously protects you from your mistake, it's a mistake nonetheless.
Your implementation of TerminateThread : Boolean; replicates existing functionality built into TThread. Instead of reinventing the wheel, use what Delphi has already provided.
I cannot see where you declared or are setting bTerminateFlag. My hunch is it's global. Using globals with multiple threads is like juggling flaming torches while standing in a room filled with open barrels of gunpowder.
Some guesses
I can hazard some guesses based on what you are trying to do in the code you have shown.
It looks like you're updating TsGuage instances to visually indicate the signal strength for each device. This is a GUI update that must be synchronised.
The line FZylGSM.ExecuteATCommand('AT+CSQ', SL_AT); seems to be the place where you interact with the device. It's probably also the slowest and what you want to processes off the main thread. This should not be synchronised if possible. However, it as indicated earlier, the feasibility of doing so depends on the implementation of that component.
That said, it seems the only line you should be synchronising is: SignalGauge.Progress := SignalStrength;.