Client-Server Communication using FIFOs for more then 1 clients

spatlou

Minutes of Meeting:
Client Server using FIFO.

dgoel735

Two issues that i was facing while creating communication using FIFOs for more than 1 clients :-

1. When more than 1 client is made, server can't able to notice which client is sending addition request , subtraction request and result gets over-written.

2. The client gets the result, server finishes all the operation and after that server does not finishes but at the end hanging of server occurs.

surajk1164

Client server project using 3 clients has been done. Below is the code for server :

#include"headers.h"
#include"prototypes.h"
#include"request.h"

void main()
{
int fd,ret,ac,*ptr,count1,sum,*ptr1;
char crfd[4],cwfd[4],crfd1[4],cwfd1[4];
request r;
ptr = creatpipe();

sprintf(crfd,"%d",*(ptr+0));
sprintf(cwfd,"%d",*(ptr+1));
sprintf(crfd1,"%d",*(ptr+2));
sprintf(cwfd1,"%d",*(ptr+3));

while(1)
{
fd = open("myfifo",O_RDONLY);
if(fd==-1)
{
perror("mkfifo");
exit(EXIT_FAILURE);
}
count1=read(fd,&r,sizeof(request));
if(count1==-1)
{
perror("read");
exit(EXIT_FAILURE);
}

count1 = write(*(ptr+1),&r,sizeof(request));
if(count1==-1)
{
perror("write");
exit(EXIT_FAILURE);
}
ret = fork();
switch(ret)
{
case 0:
invoke_req(ptr);
break;
default :
wait(&ac);
{
count1 = read(*(ptr+2),&sum,sizeof(int));
if(count1==-1)
{
perror("read");
exit(EXIT_FAILURE);
}

if(access("resfifo",F_OK)==-1)
{
mkfifo("resfifo",0666);
}
fd = open("resfifo",O_WRONLY);
count1 = write(fd,&sum,sizeof(int));
if(count1==-1)
{
perror("read");
exit(EXIT_FAILURE);
}
}
}
}
}
And client code is of following:

#include"headers.h"
#include"request.h"
int main()
{
request r;
int count,ret,count3,fd,fd1,result,ac;
r.opend1 = 20;
r.opend2 = 23;
r.opr = '*';
//r.pid = getpid():
if(access("myfifo",F_OK)==-1)
{
mkfifo("myfifo",0666);
}
fd = open("myfifo",O_WRONLY);
count3 = write(fd,&r,sizeof(request));
if(count3==-1)
{
perror("write");
exit(EXIT_FAILURE);
}
if(access("resfifo",F_OK)==-1)
{
mkfifo("resfifo",0666);
}

fd1 = open("resfifo",O_RDONLY);
count = read(fd1,&result,sizeof(int));
if(count==-1)
{
perror("read");
exit(EXIT_FAILURE);
}
printf("client seeking for multiply : %d\n",result);

return 0;
}

keshavmehta15

@surajk1164

Is your code working fine for the 3 clients when they are receiving result simultaneously or parallelly ?

It is not working in my case as when I run 3 clients simultaneously using ./client1 & ./client2 & ./client3 then my results are getting intermixed and every time different clients begin first.

But results are fine when they run individually.

Anyone having any clue regarding this problem ?

ra9501576600

@keshavmehta15

It is synchronization problem.

When one client is writing to server, server is computing the result and writing it back to client. But, as all 3 clients are working simultaneously, so it means that all 3 clients are ready to read the result from server. So, we never know which client is chosen by scheduler to get entertained. So, the correct result is coming from server, but probability that it will be received by the correct client is just 1/3 (in case of 3 clients). Client may receive the correct result, or may not be.....

Client requests are written into the fifo randomly (without any pre-defined order), and results are also not written into the clients as per the same order as above. Thus synchronization problem is caused.

dgoel735

Size of structure pointer is 8 byte for 64-bit operating system whereas 4 byte for 32-bit operating system.

dgoel735

The issues are resolved by using semaphores,signal handlers. Semaphores are used at the shared region so that one process at a time can used the shared region and no over written of data occurs.

dgoel735

Facing one more issue:

I have used shared memory for sending the request by the clients to the server and message queue for receiving the result and in adder,multiplication,subtraction and division function i have used pipes first for sending the request by the server. The shared memory data is written into the pipe but data cannot be read by any of the functions(adder,subtract,multiplication or division), maybe somewhere it gets block. Because I have checked the structure data after it was written into a pipe the data written was accurate which client had sent but while on the reader side it shows the number of bytes readed but I'm unable to access the structure data, no printf statements worked and if I remove those printf statements then also the functions did not worked till end,after reading the number of bytes it got stuck and the reading and writing/reading on pipes/FIFO is not proper because if the writer is writing the data, then reader is reading but again the printf statements of writer shows and reader gets maybe blocked. Then, I have replaced the pipes with FIFO but same problem arises.

keshavmehta15

AFTER USING SEMAPHORES:>

ISSUE IN SEMAPHORES

My project is working fine when I run my script for one time but it fails to give desired results when run on second time .......... it goes into the clients' process in second time but doesn't able to read result and also clients are not able to receive signals when run on second time . I have unlinked REQFIFO and RESFIFO after result read by server also closed file descipters where necessary . When i press ctrl+c then it is giving garbage and sometimes giving intermixed value.

I think i need to know where i should unlink REQFIFO and RESFIFO.

If anybody understood please comment below :-

gauravchopra284

@keshavmehta15

I think there is some synchronisation problem in your project. You should try to use "kill" system call before opening and writing the RESFIFO in the server and in client side, opening and reading the RESFIFO should be done inside the flag which is set and reset by the Signal Handler.

rahul.kushwaha2695

i have used message que. in following ways

struct result

{

long pid;

int res;

}d;

d.pid=getpid();

d.res=100;

msgsnd(msgid,&d,sizeof(result),IPC_NOWAIT); //msgget already done with msgid

The problem is that it gives an error of "No message of desired type".

keshavmehta15

@rahul.kushwaha2695

I think you should set your flag =0; as may be it is n't able to send because of garbage content so you should send it after "ipcrm -a" to remove msgid.

surajk1164

@rahul.kushwaha2695

Rahul check your Structure ! You have used used typedef and then giving the name 'd '
to structure ... Now this. 'd' will behave as a data type of your Structure.... Further you have assigned values just pointed by 'd' , this 'd' is a data type ....

You should give a variable name of your Structure ..
For Example...

d result
Now put values in this variable---

result.pid = getpid();
result.res = 100;

Then you should use this variable in your messagequeue like below :

msgsnd(msgid,&result,sizeof(result),IPC_NOWAIT);

abhinandan468v

server client project

3 clients are running using pipes only.

client 1 for addition.

client 2 for subtraction.

client 3 for multiplication.

FIFO implementation are under process.

challenges facing is implementation of signal in project

pankajsolanki555

Abstract : Client-Server communication by using PIPE, FIFO and Signal

Task Completed :

1. Server communication with single client with the help of PIPE.

2. Server communication with 3 clients by using PIPE.

3. Server communication with 3 client by using FIFO for sending requesting from client and receive request using pipe.

4.
Server communication with client by using FIFO to send request by
client and receive response from server with the help of signal handler.

Next Challenge :

Since 3 clients are communicating fine with the server so next challenge is to run 1000 clieint with server.

ankitvats846

1) client - server communication is done through pipe (using pipe() call);

2) server creat pipe for communication between client process and vendor process

3) corresponding file descriptor of pipes are pass to client and vendor .

4) for client two fd read and write of different pipes are pass using execl () call from child in server

5) 21 client are successfully communicating with server..

challenges :-

1) communication using FIFO..

2) deal with signal generated by kernal..

hitesh.arora1997

server creat pipe for communication between the process and vendor

i have been successfully recieved the answer from the first client

1 client has been successfully communicating to server

challenges

i am yet to use the fifo in place of the first pipe

(communication through pipes)

use of signal is also pending

mayankrohilla17

1:created pipe successfully.
2:using the concept of pipes in client server communication to run 1client.
3:using the conecpt of pipes in client server communication to run 3clients.
4:successfully run 10 clients.
Next challenge is to implement FIFO and signals

dhannjayv1996

ABSTRACT

1- we have created pipes.

2-in server we have forked the process.

3- in child we have excel the client and vendor process and we have passed the read and write file descriptor.

4-client process is writing the request which is read in the server process.

5- in server process the request sent by client write to the vendor process, vendor reads the request and perform the operation and again write the result to the server.

6- server reads the result written by the vendor and writes it to the client using write fd.

7- in client process the result is read by the client.

8- server is communicating the 3 clients and 3 vendors

All the above process is done by the pipes only.

3 clients are running successfully using pipes only.

FIFO is not implemented in the project yet.

jayshreemundrika

1 created a server ,in the server process created 4 pipes.

2 In the server process we have forked

3 I have execl in the child process client process and passed read and write fd .

4 again fork the process

5 I have execl in the child process and passed read and write fd to the vendor.

6 in the client process writing a request to the server and server reads the request.

ashishphour6

first we implement pipes.

firstly we fork() and execl() then go to client.

we are taking two pipe in client .

then
we send data by client with help of write file discriptor(wfd) then
server read data from client with read file discriptor(rfd).

then server send data to vendor then vendor read data and then write to server.

then server send data to client side.

we successfully run 1 clent with this process.

after this process repeat again fork() and execl()

i have run 10 client.

jyotipandey9813

TOPIC :Facing Ploblem during avoiding zombies .

Hi all ,

in project 003, to avoid zombies , trap a SIGCHLD ,and in its signal handler ,issue the wait3 system call with WNOHANG option.

by using this approach i am able to avoid zombies but i have faced following new problem ,

in server , i have implemented a thread semaphore ,apply sem_wait before creating a new thread and release this semaphore(sem_post) in processReq (thread ) after opening the fifo.

after running a handler , the sem_wait generate a error : Interrupted system call

for better understanding please go through my code once.

jyotipandey9813

///**server.c**//

#include"../Common/header.h"

#include"../Common/dataStruct.h"

#include"declaration.h"

Infra *infra;

sem_t thCrSem;

sem_t *pipeSem;

sem_t *vendorSem;

pthread_t ptid;

int main()

{

int res,ret;

printf("%s : BEGIN\n",__FILE__);

init();

infra=NULL;

pthread_attr_t attr;

ret=pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

if(ret == -1)

{

perror("pthread_attr_setdetachstate");

exit(EXIT_FAILURE);

}

ret=pthread_attr_init(&attr);

if(ret == -1)

{

perror("pthread_attr_init");

exit(EXIT_FAILURE);

}

signal(SIGINT,shutDown);

infra=(Infra*)(*fptr[0])((void*)infra);

ret=sem_init(&thCrSem , 0 , 1);

if(ret == -1)

{

perror("seminit 1 :");

exit(EXIT_FAILURE);

}

printf("%s : SemaPhore Initialized Successfully\n",__FILE__);

while(1)

{

if(sem_wait(&thCrSem)==-1)

{

perror("semwait : ");

exit(EXIT_FAILURE);

}

res = pthread_create(&ptid,&attr,fptr[5],(void*)infra);

if(res != 0)

{

printf("pthread_create");

exit(EXIT_FAILURE);

}

printf("%s END\n",__FILE__);

return 0;

}

jyotipandey9813

//**processReq**//

#include"../Common/header.h"

#include"../Common/dataStruct.h"

#include"declaration.h"

void chld_fun(int signum , siginfo_t *info, void *arg)

{

int pid;

while((pid = wait3(0 , WNOHANG ,0)) != - 1);

printf("\ninvoked Handler\n");

}

void* processReq(void *arg)

{

int fd,ret;

pid_t pid;

char spfd[4];

Infra *linfra = NULL;

Request a;

Result *r = NULL;

//registering the signal

struct sigaction act;

act.sa_flags = SA_SIGINFO|SA_NOCLDWAIT;

act.sa_sigaction = &chld_fun;

sigaction(SIGCHLD , &act , NULL);

printf("%s : BEGIN\n",__FILE__);

linfra = (Infra*)arg;

fd =open(linfra->fifoName ,O_RDONLY);

if(sem_post(&thCrSem)==-1)

{

perror("open");

exit(EXIT_FAILURE);

}

do

{

ret = read(fd , &a , sizeof(Request));

}

while(ret == 0);

close(fd);

pid = fork();

switch(pid)

{

case -1:

perror("fork");

exit(EXIT_FAILURE);

case 0:

sprintf(spfd , "%d" , *(linfra->pipefd+0));

printf("spfd = %s\n",spfd);

switch(a.opr)

{

case '+' :

execl("./adder","adder",spfd,NULL);

break;

default:

printf("Ooops , Invalid choice\nPlease Try Again !\n");

}

printf("failed to invoke vendor\n");

exit(EXIT_FAILURE);

default:

sem_wait(pipeSem)

write(*(linfra->pipefd+1) , &a , sizeof(Request));

sem_wait(vendorSem)

r = (Result*)linfra->smPtr;

printf("server :Result %f\n",r->res);

printf("server :Result_pid %ld\n",r->pid);

}

msgsnd(linfra->msgQue,(void*)r,sizeof(Result),0);

kill( r->pid ,SIGUSR1 );

printf("%s : END\n\n",__FILE__;

pthread_exit("Server Thread_Exit Successfully");

}

Client-Server Communication using FIFOs for more then 1 clients

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