Hi,
Thank you I would try with the configuring libevent for multithreading. Mark
also has the same suggestion.
Regarding, syncronize & connection close event. In actual code it is
implemented properly. My bad I did not do that in the sample code.
Regards,
Alap
________________________________
From: Nir Soffer <nir...@gmail.com>
To: libevent-us...@freehaven.net
Sent: Thursday, May 31, 2012 10:11 AM
Subject: Re: [Libevent-users] Crash in evhttp_send_reply_chunk()
The example code you sent is expected to crash and burn randomly:
- You use multiple threads, but you do not configure libevent to use
multithreading
- You do not synchronize the threads in your own code. For example, accessing
startSend and req from multiple threads.
- You do not handle the connection close event - it should stop the sendChunk
thread.
I suggest to use the event loop - Instead of the sendChunk thread, keep a 5
seconds timeout event for each connected client. Each time the timer runs, send
a chunk if available.
On Wed, May 23, 2012 at 5:24 PM, Alap Kumar Sinha <ala...@yahoo.com> wrote:
Hi,
>
>I am using libevent to implement a HTTP server. I am
observing a crash & connection disconnect in libevent in the following scenario.
>
>1. The process starts a libevent HTTP server &
registers for callbacks for different URLs.
>2. For one of the GET request from the client, the
server needs to keep the connection open & send chunk replies as when data
from some other source arrive.
>3. So it does a *_reply_start() & then *_reply_chunk()
when data is available
>
>Everything works fine at the beginning , but after a while
(random could in 30 mins or couple of hours) observe the following issues
>
>1. 1.The libevent crashes. Checked the core dump
analysis of multiple crashes & it points to the following code.
>
>a. 0x0042b0a8
in evbuffer_add_buffer (outbuf=0x4924b8, inbuf=0x496428) at buffer.c:774
>
>2. Sometimes
the connection between server & client gets disconnected. When checked
through wireshark, observed a FIN ACK coming from the HTTP server.
>
>
>Below is a simplified code snippet showcasing the implementation
& use case.
>
>I would appreciate if someone could let know, if I am
doing something wrong in the usage of the libevent APIs & what could be the
cause of the crash.
>
>#define KEY_STRING "CHECK"
>
>
>struct evhttp_request *req; //Structure holds the req, on which chunk reply
>is sent
>
>
>pthread_t SenderThread;
>bool startSend = false;
>
>void connectionClosed(struct
evhttp_connection* evcon, void* key)
>{
> printf("Connection
closed by client");
>}
>//****** Function to send some data every 5 secs************/
>
>void sendChunk(struct evhttp_connection*
evcon, void* key)
>{
> int
counter = 0;
> printf("Start
sending data everyy 5 secs");
> while(1)
> {
>
> if(startSend)
//startSend is set to true when client does a GET & SSEEvents_cb() is
invoked
> {
> evbuffer
*databuf = evbuffer_new();
> if
(databuf != NULL)
> {
>
>evbuffer_add(databuf,"event:remoteEvent\n",strlen("event:remoteEvent\n"));
>
>evbuffer_add_printf(databuf,"data:TestDATA%d\n",counter);
>
> evhttp_send_reply_chunk(req,
databuf);
> evbuffer_free(databuf);
> counter++;
> if(10000 == counter)
> counter = 0;
>
> }
> sleep(5);
> }
> else
> {
> sleep(2); //Sleep for 2 secs & then check if
>the flag is set or not
>
> }
>
>
>
> }
>}
> ///******Callback when Client does a GET on URL "/SSEEvents"********
>
>
>void SSEEvents_cb(struct evhttp_request
*aReq, void *key)
>{
>
> if
(EVHTTP_REQ_GET == aReq->type)
> {
> const
char * getUri = evhttp_request_get_uri(aReq);
> if(
NULL == getUri )
> {
> evhttp_send_reply(aReq,
400, "Bad request", NULL); //Response
back to client
> }
>
> req
= (evhttp_request*) aReq;
>
> evhttp_request_own(aReq);
>
>
>evhttp_connection_set_closecb(evhttp_request_get_connection(aReq),&connectionClosed,
KEY_STRING);
>
>
>evhttp_add_header(aReq->output_headers,"Content-Type","text/event-stream");
//Mandatory
> evhttp_send_reply_start(aReq,
200, "OK"); ///Start the reply & then set the flag so that chunk reply can be
sent every 5 secs
>
>
> //
Set this flag to true so that the sender thread can start sending chunk data
> startSend
= true;
>
> }
> else
> {
> evhttp_send_reply(aReq,
501, " SET Not Implemented", NULL);
> }
>}
>int StartServer(char *aIPAddress, char
*aPort)
>{
> base
= event_base_new();
> if
(!base)
> {
> printf("Couldn't
create an event_base: So Exiting");
> return
1;
> }
>
> /*
Create a new evhttp object to handle requests. */
> http
= evhttp_new(base);
> if
(!http)
> {
> printf("Couldn't
create evhttp: So Exiting....");
> return
1;
> }
> //Register
for callback for any HTTP request for url "SSEEvents"
> evhttp_set_cb(http,
"/SSEEvents", SSEEvents_cb, this);
>
> /*
Now we tell the evhttp what port to listen on */
> uint16_t
port = atoi(aPort);
> handle
= evhttp_bind_socket_with_handle(http, aIPAddress, port);
> if
(!handle)
> {
> printf("couldn't
bind to IP & port %d. Exiting.",(uint16_t)port);
> return
-1;
> }
> ///**
Launch Thread to send chunk reply after http client makes request
> pthread_attr_t
attr;
> pthread_attr_init(&attr);
> pthread_attr_setstacksize(&attr,
(128 * 1024)); //128kbs
> int
threadCreate = -1;
> threadCreate
= pthread_create(&SenderThread, NULL, &sendChunk, NULL);
>
> event_base_dispatch(base);
> return
0;
>}
>int main(int argc , char *argv[])
>{
> StartServer(argv[1],
argv[2]);
>}
>
>
>Regards,
>Alap
>
