MultiThreaded FastCGI App Server

[Miguel Pando]

Hello everyone.

I am writing a little multithreaded FastCGI server, which i would like to describe
briefly, and get your constructive criticism.

Creates a modeless dialog with 2 buttons, OK(go) button, Stop button.
Then hides and shows an icon in the taskbar.

Creates a fixed number(configurable) of worker threads in Suspended state.
A FastCGI server should not be running on a single thread.

Creates a circular Queue. This is an array of requests(FCGX_Request)
coming from WebServer, with 2 pointers. One points to next available
slot, the other to next unprocessed slot(Request). The size of this
array is 5 slots(default) times number of worker threads.

Program sets Above-Normal priority to main thread. This thread is in a
PeekMessage loop, waiting for messages like user input(Stop/Go) events,
or Suspend inactive thread commands. If no message pending, sleeps for
(number of threads * 25) milliseconds.

Creates an Accept Request Thread(Dispatcher), also at Above-Normal priority.
This thread is in a loop waiting for requests(FCGX_Accept_r). When a
new request is received, if a thread is available(Suspended) it Resumes
that thread to handle this request. If all threads are busy it just lets
the new request in the circular queue. This allows to accept more requests
than worker threads.

When a worker thread is ready(Resumed) to handle a request, it calls Handlerequest
procedure in HandlReq.dll, passing that procedure a pointer to FCGX_Request.
This procedure must be ThreadSafe. In this Handlreq.dll all HTML output
should be created and sent to WebServer. This separates the FastCGI server
from the application DLL.

When a worker thread finishes handling a request, it looks in the queue
for another request(Synch by Mutex), if none available it goes back to
Suspended state by sending message to main thread to suspend itself.

I am testing this server with the Abyss WebServer, but under very light load.
Anything wrong with the overall design, performance, or any other issue?
I thank you very much for your comments, and opinions. I know there are many
competent programmers in this forum.

Thank you

[Miguel Pando]

I think one of the main issues in this FastCGI server is the
technique of suspending, resuming the worker threads. The worker
threads are always kept in a loop, calling on any type of(ThreadSafe) App DLL.

DECLARE FUNCTION HandleRequest LIB "HANDLREQ.DLL" (req AS FCGX_Request) AS LONG
'***************************************************************
FUNCTION thread_run(BYVAL i AS LONG) AS LONG
'***************************************************************
LOCAL e AS LONG, ix AS LONG
        DO
           IF threads(i, 1)=-1 THEN EXIT DO
           ix=cq_dequeue()                      'Look into Circular Queue
           IF ix>0 THEN                         'FCGI_Request Available
                e=HandleRequest(cq(ix))         'Call ANY Application DLL
           ELSE
                IF quitflag THEN
                        threads(i, 1)=-1
                        check_running
                        EXIT DO
                END IF
                SendMessage hDlg, %THREAD_SUSPEND, 0, i   'To MAIN thread
           END IF
        LOOP
        thread_run=-1
END FUNCTION
'***************************************************************
'DOEVENTS - MAIN THREAD
CALLBACK FUNCTION xDialog()
'***************************************************************
        CASE %THREAD_SUSPEND
                i=CBLPARAM
                THREAD SUSPEND threads(i, 0) TO x
                threads(i, 1)=0
END FUNCTION

Not sure if this is the most efficient performance wise.

Another issue is keeping more requests than available threads.
No need for excessive number of threads. This could be a key point.

'***************************************************************
SUB get_thread()        'Called by Acceptreq Thread
'***************************************************************
LOCAL i AS LONG, x AS LONG
    FOR i=1 TO nthreads
        IF threads(i, 1)=0 THEN EXIT FOR  'Thread available
    NEXT i
    IF i>nthreads THEN                    'All worker threads Busy
        i=0                               'Keep FCGX_Request in Circular Queue
    ELSE
        threads(i, 1)=1
        THREAD RESUME threads(i, 0) TO x  'Wake first available thread
    END IF
END SUB

I appreciate very much your commnents on this work.

[RyanCross]

Sample?

I am kind of confused on how FastCGI works. I have downloaded DLL the samples from http://www.coastrd.com/.

I compile the samples and then try to run them and all I get is ERROR 500.

Using the latest Abyss Web Server I added the virtual path /cgi-bin/*.exe to the Scripting Parameters and made it Fast CGI (Local - Pipes).

I get this error in my Fast CGI log:
Writing 5392 bytes failed = The process cannot access the file because it is being used by another process.

[Miguel Pando]

Hello

Now i realize there is no need for the modeless window and the PeekMessage loop.

I was confused with the fact that the Main Thread is running in Above-Normal priority.

So now the window is modal, and there is no PeekMessage loop. When the
user press the Stop button a FCGC_Shutdownpending is executed and a
Dialog End breaks the modal window.

After that, the main thread resumes worker threads that are Suspended,
so they break out of their loop, and exit.

Bye