deadlock between IoTHubClient_UploadToBlobAsync and IoTHubClient_SendEventAsync when used with DeviceMethodCallback

[N6UDP]

I seem to be getting a deadlock between IoTHubClient_UploadToBlobAsync and IoTHubClient_SendEventAsync when used with DeviceMethodCallback. Platform is MIPS Linux. As requested in #26 here is a repro:

#define _BSD_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

#include "azure_c_shared_utility/threadapi.h"
#include "azure_c_shared_utility/crt_abstractions.h"
#include "azure_c_shared_utility/platform.h"
#include "iothub_client.h"
#include "iothub_message.h"
#include "iothubtransportmqtt.h"

static int callbackCounter;
IOTHUB_CLIENT_HANDLE iotHubClientHandle;
typedef struct EVENT_INSTANCE_TAG
{
    IOTHUB_MESSAGE_HANDLE messageHandle;
    size_t messageTrackingId;  // For tracking the messages within the user callback.
} EVENT_INSTANCE;

void takepicture(void);
static int DeviceMethodCallback(const char* method_name, const unsigned char* payload, size_t size, unsigned char** response, size_t* resp_size, void* userContextCallback)
{
    (void)userContextCallback;
    int status = 200;
    printf("\r\nDevice Method called\r\n");
    printf("Device Method name:    %s\r\n", method_name);
    printf("Device Method payload: %.*s\r\n", (int)size, (const char*)payload);
if(strcmp(method_name,"takepicture")==0){
        takepicture();
    }
  char* RESPONSE_STRING = "{ \"Response\": \"Nothing\" }";
    printf("\r\nResponse status: %d\r\n", status);
    printf("Response payload: %s\r\n\r\n", RESPONSE_STRING);

    *resp_size = strlen(RESPONSE_STRING);
    if ((*response = malloc(*resp_size)) == NULL)
    {
        status = -1;
    }
    else
    {
        (void)memcpy(*response, RESPONSE_STRING, *resp_size);
    }

    return status;
}
static void SendConfirmationCallback(IOTHUB_CLIENT_CONFIRMATION_RESULT result, void* userContextCallback)
{
    EVENT_INSTANCE* eventInstance = (EVENT_INSTANCE*)userContextCallback;
    (void)printf("Confirmation[%d] received for message tracking id = %zu with result = %s\r\n", callbackCounter, eventInstance->messageTrackingId, ENUM_TO_STRING(IOTHUB_CLIENT_CONFIRMATION_RESULT, result));
    callbackCounter++;
    IoTHubMessage_Destroy(eventInstance->messageHandle);
}
void takepicture(void){
 long length = 0;
    unsigned char* imagebuffer = NULL;
    FILE* fo = fopen("/tmp/snap.jpg", "r");

    if(fo)
    {
        fseek(fo, 0, SEEK_END);
        length = ftell(fo);
        fseek(fo, 0, SEEK_SET);

        if(length)
        {
            imagebuffer = (unsigned char *)malloc(length*sizeof(unsigned char));
            fread(imagebuffer, length, 1, fo);
            printf("its %ld long\n",length);
            if (IoTHubClient_UploadToBlobAsync(iotHubClientHandle, "file.jpg", (const unsigned char*)imagebuffer, length, NULL, NULL) != IOTHUB_CLIENT_OK)
            {
                printf("Image failed to upload\n");
            }
            else
            {
                printf("Image has been created\n");
            }
        }
        fclose(fo);
        free(imagebuffer);
    }
}
void loop(void)
{

    EVENT_INSTANCE messages[MESSAGE_COUNT];
    int receiveContext = 0;


    callbackCounter = 0;

    if (platform_init() != 0)
    {
        fprintf(stderr,"Failed to initialize the platform.\r\n");
        exit(1);
    }
    if ((iotHubClientHandle = IoTHubClient_CreateFromConnectionString("YOURSTRINGHERE", MQTT_Protocol)) == NULL)
    {
        (void)fprintf(stderr,"ERROR: iotHubClientHandle is NULL!\r\n");
        exit(1);
    }
    bool traceOn = true;
    IoTHubClient_SetOption(iotHubClientHandle, "logtrace", &traceOn);


    if (IoTHubClient_SetDeviceMethodCallback(iotHubClientHandle, DeviceMethodCallback, &receiveContext) != IOTHUB_CLIENT_OK)
    {
        (void)fprintf(stderr,"ERROR: IoTHubClient_SetMessageCallback..........FAILED!\r\n");
        exit(1);
    }

    (void)printf("IoTHubClient_SetMessageCallback...successful.\r\n");

    /* Now that we are ready to receive commands, let's send some messages */
    size_t iterator = 0;
    do
    {
    
         const char* msgText = "test";

             
                if ((messages[iterator].messageHandle = IoTHubMessage_CreateFromByteArray((const unsigned char*)msgText, strlen(msgText))) == NULL)
                {
                    (void)fprintf(stderr,"ERROR: iotHubMessageHandle is NULL!\r\n");
          exit(1);
                }
                else
                {
                    MAP_HANDLE propMap;

                    messages[iterator].messageTrackingId = iterator;

                    propMap = IoTHubMessage_Properties(messages[iterator].messageHandle);
                    (void)sprintf_s(propText, sizeof(propText), "PropMsg_%zu", iterator);
                    if (Map_AddOrUpdate(propMap, "PropName", propText) != MAP_OK)
                    {
                        (void)fprintf(stderr,"ERROR: Map_AddOrUpdate Failed!\r\n");
                    }

                    if (IoTHubClient_SendEventAsync(iotHubClientHandle, messages[iterator].messageHandle, SendConfirmationCallback, &messages[iterator]) != IOTHUB_CLIENT_OK)
                    {
                        (void)fprintf(stderr,"ERROR: IoTHubClient_SendEventAsync..........FAILED!\r\n");
                        exit(1);
                    }
                    else
                    {
                        (void)printf("IoTHubClient_SendEventAsync accepted message [%zu] for transmission to IoT Hub.\r\n", iterator);
                    }

                }
                }else {(void)printf("ERROR: NoDataFromGetInfo..........FAILED!\r\n");}
            } 
        }
        if(iterator % 20 == 0) {
            takepicture(); // This works oddly enough
        }
        ThreadAPI_Sleep(20000);
iterator++;

    } while (true);

    IoTHubClient_Destroy(iotHubClientHandle);

    platform_deinit();

}
int main(void)
{
    loop();
    return 0;
}

[mhshami01]

Hello @N6UDP

Thank you for your submission. I am investigating your report.

Best Regards,
Haitham Shami

[mhshami01]

Hello @N6UDP,

I have recently checked in master branch fixes that would allow IoTHubClient_UploadToBlobAsync to be called from inside a device_method_callback function.

I am hoping this unblocks you. If you still encounter issues, please reply here.

Best Regards,
Haitham Shami