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Fix reference example in README #18

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Dec 18, 2020
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Fix reference example in README #18

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22 changes: 15 additions & 7 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -20,13 +20,14 @@ See memory requirements for this library [here](https://docs.aws.amazon.com/embe

## Reference example

The example below shows how to use the backoffAlgorithm library to retry a DNS resolution query for `amazon.com`.
The example below shows how to use the backoffAlgorithm library on a POSIX platform to retry a DNS resolution query for `amazon.com`.

```c
#include "backoff_algorithm.h"
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <unistd.h>
#include <time.h>

/* The maximum number of retries for the example code. */
Expand All @@ -44,11 +45,11 @@ int main()
BackoffAlgorithmStatus_t retryStatus = BackoffAlgorithmSuccess;
BackoffAlgorithmContext_t retryParams;
char serverAddress[] = "amazon.com";
uint16_t nextRetryBackOff = 0;
uint16_t nextRetryBackoff = 0;

int32_t dnsStatus = -1;
struct addrinfo hints;
struct addrinfo ** pListHead;
struct addrinfo ** pListHead = NULL;
struct timespec tp;

/* Add hints to retrieve only TCP sockets in getaddrinfo. */
Expand Down Expand Up @@ -86,12 +87,19 @@ int main()
{
/* Generate a random number and get back-off value (in milliseconds) for the next retry.
* Note: It is recommended to use a random number generator that is seeded with
* device-specific entropy source so that backoff calculation in devices is different
* device-specific entropy source so that backoff calculation across devices is different
* and possibility of network collision between devices attempting retries can be avoided.
*
* For the simplicity of the code example, the pseudo random number generator, rand() function
* is used. */
retryStatus = BackoffAlgorithm_GetNextBackoff( &retryParams, rand(), &nextRetryBackOff );
* For the simplicity of this code example, the pseudo random number generator, rand()
* function is used. */
retryStatus = BackoffAlgorithm_GetNextBackoff( &retryParams, rand(), &nextRetryBackoff );

/* Wait for the calculated backoff period before the next retry attempt of querying DNS.
* As usleep() takes nanoseconds as the parameter, we multiply the backoff period by 1000. */
( void ) usleep( nextRetryBackoff * 1000U );

/* Retry the DNS lookup for the host name. */
dnsStatus = getaddrinfo( serverAddress, NULL, &hints, pListHead );
}
} while( ( dnsStatus != 0 ) && ( retryStatus != BackoffAlgorithmRetriesExhausted ) );

Expand Down