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Example of using Queue to pass strings between tasks

https://esp32.com/viewtopic.php?f=18&t=3086

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Re: Example of using Queue to pass strings between tasks

Posted: Mon Oct 15, 2018 6:37 am
by sam@logic
kolban wrote:To create a queue, you would use xQueueCreate ... see http://www.freertos.org/a00116.html

The size parameter would be large enough to hold a pointer to a character string ... for example:

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sizeof(char *)
When you have a string to place on the queue:

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char *myData = "helloWorld";
you could then allocate enough storage for it and copy it in:

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char *myItem = malloc(strlen(myData)+1); 
strcpy(myItem, myData);
You could then push the item onto the queue using xQueueSendToBack() ... see http://www.freertos.org/xQueueSendToBack.html

for example,

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xQueueSendToBack(myQueue, &myItem, portMAX_DELAY);
When you wish to receive an item ...

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char *myReceivedItem;
xQueueReceive(myQueue, &myReceivedItem, portMAX_DELAY);
// Do something with received string and then delete it ...
free(myReceivedItem);
See: http://www.freertos.org/a00118.html
Hi,
I want to send and recieve multiple strings to/from queue.
but as I send strings in queue one by one in one task and receive in other task, on recieve task it is only receiving first string that is sent on queue. I am getting what is the problem. please help me out for this problem.
below is my code.

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#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/queue.h"
#include "string.h"

#define BUF 1024
xQueueHandle xQueue;


void consumer_task(void *pvParameter)
{
    char* rxmesage;


    while(1){
    	if( xQueue != 0 ) {

			if( (xQueuePeek( xQueue, &( rxmesage ), ( portTickType ) 10 )) == pdTRUE)
			{
			   printf("value received on queue: %s \n",rxmesage);
			   vTaskDelay(1500/portTICK_PERIOD_MS); //wait for 500 ms
			}
    }
    }
}

void producer_task(void *pvParameter){

	char *mydata="scanData={\"priority\":\"Normal\",\"device\":\"Reader1\",\"event\":\"STRAY\",\"timeStamp\":\"10/8/2018 11:16:10 PM\",\"scanItems\":[{\"thing\":\"%d%d\",\"deviceName\":\"%s\",\"mfid\":\"%X%X\",\"aid\":\"%u\",\"rid\":\"%u\",\"rssi\":%s,\"txPower\":%d,\"battery\":%u,\"scanTime\":\"25/8/2018 11:16:10 PM\",\"scanCount\":1,\"additionalData\":{\"mov\":\"%u\",\"temp\":%d,\"humidity\":%u,\"pressure\":\"%u\",\"location\":null}}],\"message\":\"Test\"}";
    char  *repl_data="";
    int count=0;
    while(1){
		 asprintf(&repl_data,"%d %s",count,mydata);
		 printf("value sent on queue: %s \n",repl_data);
         xQueueSend(xQueue,(void *)&repl_data,(TickType_t )0); // add the counter value to the queue

         vTaskDelay(500/portTICK_PERIOD_MS); //wait for a second
         count++;

    }
}

void app_main()
{
	uint8_t* dataSerial = (uint8_t*) malloc(BUF);
	xQueue = xQueueCreate( 1, sizeof(dataSerial));
    if(xQueue != NULL){
        printf("Queue is created\n");
        vTaskDelay(1000/portTICK_PERIOD_MS); //wait for a second
        xTaskCreate(&producer_task,"producer_task",1024*4,NULL,5,NULL);
        printf("producer task  started\n");
        xTaskCreate(&consumer_task,"consumer_task",1024*4,NULL,5,NULL);
        printf("consumer task  started\n");
    }else{
        printf("Queue creation failed");
    }
}

Re: Example of using Queue to pass strings between tasks

Posted: Mon Oct 15, 2018 9:33 am
by burkulesomesh43
Hi,
Is the queue data can be stored only in runtime??
after reset of esp32, it losses data stored in queue??

Re: Example of using Queue to pass strings between tasks

Posted: Tue Oct 16, 2018 2:54 am
by ESP_Sprite
Yes, queues in the end are just memory structures like all other FreeRTOS structures, and they'll get cleared on reset. Use NVS or RTC memory if you want to store stuff over a reset.

Re: Example of using Queue to pass strings between tasks

Posted: Wed Oct 17, 2018 5:40 am
by burkulesomesh43
ESP_Sprite wrote:Yes, queues in the end are just memory structures like all other FreeRTOS structures, and they'll get cleared on reset. Use NVS or RTC memory if you want to store stuff over a reset.
Ok. thanks

Re: Example of using Queue to pass strings between tasks

Posted: Sun Oct 21, 2018 11:22 am
by burkulesomesh43
Hi,
I am sending data stored in variable using asprintf(), but the data recieved from queue is garbage data.
I cant find what is the problem.

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char *single_tag=NULL;
int ret=asprintf(&single_tag,"Some Data:%s",data);
if(ret==-1)
 {
   ESP_LOGI(tag, "asprintf:memory allocation failed");
 }

ESP_LOGI(TAG, "single_tag:%s", single_tag);

 if(xQueueSend( xQueue, ( void * )&single_tag, ( portTickType )0 )==errQUEUE_FULL)
  {
      ESP_LOGI("Queue","Queue is full..");
  }
  	 bzero(single_tag, strlen(single_tag));
	 free(single_tag);

Re: Example of using Queue to pass strings between tasks

Posted: Sun Oct 21, 2018 4:28 pm
by chegewara
You have to initialize single_tag with malloc or similar before you can use it.

Re: Example of using Queue to pass strings between tasks

Posted: Sun Oct 21, 2018 7:01 pm
by burkulesomesh43
chegewara wrote:You have to initialize single_tag with malloc or similar before you can use it.
bur asprintf() will automatically allocate the memory...

Re: Example of using Queue to pass strings between tasks

Posted: Tue Oct 23, 2018 2:32 am
by ESP_Sprite
You should send a pointer to your data to xQueueSend to queue the data. You are sending a pointer to a pointer to the data instead, queueing the pointer. Remove the & in the xQueueSend and you should be good.

Re: Example of using Queue to pass strings between tasks

Posted: Fri Nov 02, 2018 2:15 pm
by burkulesomesh43
Hi,
How to find number of items are in queue?? is there any api?

Re: Example of using Queue to pass strings between tasks

Posted: Wed Nov 07, 2018 1:08 am
by ESP_Sprite
burkulesomesh43 wrote:Hi,
How to find number of items are in queue?? is there any api?
https://www.freertos.org/a00018.html#uc ... gesWaiting
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