I'm trying to process data from my sensors, and simultaneously, upload data to the server(Thingspeak).
The problem is, whenever server connection(using wifi) ends(and i couldn't find a way to extend my session to prevent timeout), reconnecting takes time and during that time, i can't process the data from the sensors, resulting occasional holes in my data.
I heard there's some way of resolving this problem by using callback functions, somehow making the core to wait for the response from the server each time I try to connect to server, and at the same time, process the data i'm getting from the sensor.
My code right now is like this
loop
{
while(now==prev)
{
processdata;
}
prev=now;
count++;
if(count==15)
{
count=0;
senddata();
}
}
senddata()
{
if(!serverconnected)
{
if(!send connect request()) error message; //after this function calls,
if(!receive connection confirmed()) error message; //takes too long time until this function finishes executing.
}
send data.
}
actual function names for the commented parts are
client.connect(host, port)
client,verify(fingerprint, host)
functions from
WiFiClientSecure.h
is there any way to use callback methods to fix this issue?
While searching for the solution, I found the following header file
espconn.h
which seems to have callback functions that I can use... but I'm not sure if this is using different methods of establishing wifi connections to the server, nor how to use the functions itself.
As long as you use rest api you will not be able to comfortably keep the session alive. So you better have websocket or MQTT like protocol where session is handled by them an you will be only responsible to push the data to server instantly on any time.
This link describes how an mqtt client connection to be done on Thingspeak and pushing the data to it.
Some code cuts from the link :
#include <PubSubClient.h>
WiFiClient client;
PubSubClient mqttClient(client);
const char* server = "mqtt.thingspeak.com";
mqttClient.setServer(server, 1883);
Related
I have an issue of an if statement not passing whilst my system gatt connection is not made.
Context
I have a BLE system using a NRF52840-dk board programmed in C. I also have a mobile application which, communicates with this board via a Gatt connection. I have a single service with a single characteristic. I write to this characteristic from my mobile application and, from this do some processing. At the moment I can send over a timestamp and begin storing data. However, I need to then send data back to my mobile device by this connection.
So what I have is a command to be sent from the phone to ask for some data. This should then send data back to the phone by changing the characteristic value.
Before I can change the value I need to see if the command has been issued. However, due to the priorities and constraints of the device I need to do this processing in the main function not in the BLE interrupt that I have done my time stamping in. This is due to the data I will be transmitting eventually will be large.
My issue however is, I receive the command to send some data back to the phone and update a global int value (changed from 0 to 1). Then in my main loop test this value and, if it is 1 write to the terminal and change the value back. I would then use this point of the code to run a function to send the data.
But this statement does not pass.
This is my main loop code
if(GATT_CONNECTED == false)//This works!
{
//Do some functions here
}
else if (GATT_CONNECTED == true)// GATT_CONNECTED = true
{
NRF_LOG_INFO("Test1 passed");//Testing variable this does not print
if(main_test == 1)
{
NRF_LOG_INFO("Test2 passed");//This does not print either irrelevant of value
main_test = 0;//False
}
idle_state_handle();
}
I don't know if the issue is the way I have defined my variable or due to interrupt priorities or something like that. But, when my Gatt connection is made the loop of (GATT_CONNECTED == true) does not seem to process.
My variable is defined in another file where my GATT connection is handled. The GATT connected variable is handled in main. my main_test variable is defined in another c file as int main_test = 0;. In the header declared as extern int main_test;.
I know the GATT_CONNECTED variable works as I have code in it that only runs when my gatt is not connected. I have omitted it for simplicity.
Any ideas,
Thanks
Ps Hope you are all keeping well and, safe
Edit
Added code for simplicity
main.c
bool GATT_CONNECTED = false;
int main(void)
{
Init_Routine();
while(1)
{
Process_data();//This runs if the gatt is not connected if statement inside
if(GATT_CONNECTED == true)//This does not run true when the gatt is connected
{
NRF_LOG_INFO("check gatt connectedpassed");//Testing variable.
nrf_gpio_pin_set(LED_4);//Turn an LED on once led 4 does not work
}
idle_state_handle();
}
}
I want to create to function. The first one is connect to DB, the second one is complete reconnection if first is failed.
In my experiment I turn off DB at start to get connect block failed and call reconnect block. After it I am turning on DB, and expecting that connection block will success, but I am getting exception.
Here is my code:
bool connect()
{
if(connection is null)
{
scope(failure) reconnect(); // call reconnect if fail
this.connection = mydb.lockConnection();
writeln("connection done");
return true;
}
else
return false;
}
void reconnect()
{
writeln("reconnection block");
if(connection is null)
{
while(!connect) // continue till connection will not be established
{
Thread.sleep(3.seconds);
connectionsAttempts++;
logError("Connection to DB is not active...");
logError("Reconnection to DB attempt: %s", connectionsAttempts);
connect();
}
if(connection !is null)
{
logWarn("Reconnection to DB server done");
}
}
}
The log (turning on DB after few seconds):
reconnection block
reconnection block
connection done
Reconnection to DB server done
object.Exception#C:\Users\Dima\AppData\Roaming\dub\packages\vibe-d-0.7.30\vibe-d\source\vibe\core\drivers\libevent2.d(326): Failed to connect to host 194.87.235.42:3306: Connection timed out [WSAETIMEDOUT ]
I can't understand why I am getting exception after: Reconnection to DB server done
There's two main problems here.
First of all, there shouldn't be any need for automatic retry attempts at all. If it didn't work the first time, and you don't change anything, there's no reason doing the same exact thing should suddenly work the second time. If your network is that unreliable, then you have much bigger problems.
Secondly, if you are going to automatically retry anyway, that's code's not going to work:
For one thing, reconnect is calling connect TWICE on every failure: Once at the end of the loop body and then immediately again in the loop condition regardless of whether the connection succeeded. That's probably not what you intended.
But more importantly, you have a potentially-infinite recursion going on there: connect calls reconnect if it fails. Then reconnect calls connect up to six times, each of those times connect calls reconnect AGAIN on failure, looping forever until the connection configuration that didn't work somehow magically starts working (or perhaps more likely, until you blow the stack and crash).
Honestly, I'd recommend simply throwing that all away: Just call lockConnection (if you're using vibe.d) or new Connection(...) (if you're not using vibe.d) and be done with it. If your connection settings are wrong, then trying the same connection settings again isn't going to fix them.
lockConnection -- Is there supposed to be a matching "unlock"? – Rick James
No, the connection pool in question comes from vibe.d. When the fiber which locked the connection exits (usually meaning "when your server is done processing a request"), any connections the fiber locked automatically get returned to the pool.
I am new in TCP server client program . I want to develop a application in C to authenticate client and receive data from server . I know I need to use thread to handle multiple client . But I am concern about how can I call each functions in server side via thread or any need of creating more threads in server (like worker thread to do each functions) . I have a server which has lot of function like fun1() ,fun2(),fun3(),fun4() to handle the client data .So Is it any problem or delay when I use thread ? because when multiple client come at one sec , how the server handle this case ? I develop a logic like
server fun
{
//thread function calling fun1()
}
void *fun1(void *arg)
{
fun2()
pthread_exit((void*)xx)
}
fun2()
{
fun3()
}
fun3()
{
}
When you are using C you have to use the function accept for incoming connections. accept is a blocking function, so it waits until a connection is established. The return parameter of this function is a socket.
So your next statement after accept should be a creation of a thread with the input parameter of the socket. In your thread you can call your functions fun1,fun2,...
Of course there is a little delay but it's only milliseconds. When multiple clients are going to connect, they are queued.
The advantage of a parallel Server instead of a serial server is that one client can't block your service.
Hi I am figuring out a way to listen to a socket and connect to a different socket(on same ip but different port number) simultaneously in the same program.when I listen to a socket then it keeps blocking until it receives some message so I am not able to listen and connect simultaneously.
I actually need to simulate exchange of LSP packets between different routers. So I am writing a program to simulate a router so as to run it n(number of routers)times.
Could anyone please share on how to proceed ??
If I understood your problem correctly, one of these might help.
Multi-thread or Multi-process
Basically, when you receive a client you can process a client separately in a separate thread or in a new process. You will be able to receive incoming connections and connect to new clients from other sources while processing the ones who are already connected.
Pseudo Code:
main() {
while(1) {
accept client
/*
After the fork or creation of the new thread, the loop goes back to
accepting clients while connected clients are being processed.
*/
fork or create new thread passing and client socket to it
}
}
processClient() {
do whatever you need to do...
}
Select
Select is another good way of doing non-blocking sockets. Select basically waits for data to come (ie. data, new client requests) to the server and processes them one-by-one. The server will not block on accept as it will wait until it receives something before processing it.
Psuedo Code:
main() {
while(1) {
wait on select
if new client {
accept it
}
for client in clients {
if client has data {
process it
}
}
}
}
ePoll (if you're in Linux)
ePoll is similar to Select only it can handle WAY more clients and it's a lot sexier.
Here's a repo that has each of those. My code isn't perfect here as it was a project that I did while in school.
https://github.com/koralarts/ServerBenchmarking
In my java code, I am processing huge amount of data. So I moved the code as servlet to Cron Job of App Engine. Some days it works fine. After the amount of the data increases, the cron job is not working and shows the following error message.
2012-09-26 04:18:40.627
'ServletName' 'MethodName': Inside SQLExceptionjava.sql.SQLRecoverableException:
Connection is already in use.
I 2012-09-26 04:18:40.741
This request caused a new process to be started for your application, and thus caused
your application code to be loaded for the first time. This request may thus take
longer and use more CPU than a typical request for your application.
W 2012-09-26 04:18:40.741
A problem was encountered with the process that handled this request, causing it to
exit. This is likely to cause a new process to be used for the next request to your
application. If you see this message frequently, you may be throwing exceptions during
the initialization of your application. (Error code 104)
How to handle this problem?
This exception is typical when a single connection is shared between multiple threads. This will in turn happen when your code does not follow the standard JDBC idiom of acquiring and closing the DB resources in the shortest possible scope in the very same try-finally block like so:
public Entity find(Long id) throws SQLException {
Connection connection = null;
// ...
try {
connection = dataSource.getConnection();
// ...
} finally {
// ...
if (connection != null) try { connection.close(); } catch (SQLException ignore) {}
}
return entity;
}
Your comment on the question,
#TejasArjun i used connection pooling with servlet Init() method.
doesn't give me the impression that you're doing it the right way. This suggests that you're obtaining a DB connection in servlet's init() method and reusing the same one across all HTTP requests in all HTTP sessions. This is absolutely not right. A servlet instance is created/initialized only once during webapp's startup and reused throughout the entire remaining of the application's lifetime. This at least confirms the exception you're facing.
Just rewrite your JDBC code according the standard try-finally idiom as demonstrated above and you should be all set.
See also:
Is it safe to use a static java.sql.Connection instance in a multithreaded system?