How to resend android push notification first try failed - php

Question

I have this methode :
$oAndroidService = new GoogleGNCService($message);
# divide per batch with 1000 users
$a_batch = array_chunk($a_users, 1000);
for($i = 0; $i < count($a_batch); $i++){
# get the liste of tokens
foreach($a_batch[$i] as $batch){
$a_tokens[] = $batch['token'];
}
# if push sent with success
if($oAndroidService->sendPush($a_tokens)){
foreach($a_batch[$i] as $userToProcess){
// update push token history
}
}
echo 'PUSH SENT !';
# unset the array with tokens
unset($a_tokens);
}else{
echo 'ERROR SENT PUSH'
}
}
And the method that sent pushes :
public function sendPush($a_token){
# init the curl connection
$ch = curl_init();
# if success connection
if($ch){
# array that will be send in post with curl call
$a_post = array(
'registration_ids' => $a_token,
'data' => $this->getMessage(),
);
# set the options of curl request
curl_setopt($ch, CURLOPT_URL, self::ANDROID_URL);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, $this->getHeaders());
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($a_post));
# execute the request
$result = curl_exec($ch);
if($result === false){
echo('Curl failed : ' . curl_error($ch));
return false;
}
# close the request
curl_close($ch);
return true;
}
echo 'Connection failed';
return false;
}
I have 2 questions :
If I sent 1000 tokens and curl failed, I need to resend this array with tokens one more time ? If failed the second time, I need to resent third time ?
If curl failed how to know what are the token that poses problems ?
Thx for you help in advance