SerialEvent() data losing when Timer1 ISR is running

Using Arduino Programming Questions
#1

Hello, I have an arduino code with below sections.

Section I

void Setup()
{
cli();
TCCR1A = 0;
TCCR1B = 0;
TIMSK1 |= (1 << TOIE1);
TCNT1= PRELOAD;
TCCR1B |= (1 << CS11);
TCCR1B |= (1 << CS10);
sei();
}

ISR(TIMER1_OVF_vect)
{
TCNT1=PRELOAD;
count++;
count2++;
if (count>10)
{
myDisplay.DisplayString(tempString, 0);
count = 0;
}
if(count2>604800)
{
delSMS();
count2 = 0;
}
}

Section II

void serialEvent()
{
while (Serial.available()>0)
{
char lastChar = (char)Serial.read();
IncomingData += lastChar;
int len =strlen(IncomingData.c_str());
char *p=IncomingData.c_str();
p[len-1]=’\0’;
IncomingData = p;
}
}

When the code is running, some serial readings are missing. But if I remove the first section from my code, that serial data reads well. What happens in this case. Please suggest the solution for this matter.

#2 
 char lastChar = (char)Serial.read();
      IncomingData += lastChar;
      int len =strlen(IncomingData.c_str());
      char *p=IncomingData.c_str();
      p[len-1]='\0';
      IncomingData = p;

Couldn't you decide whether to just use Strings or strings?

Please post your code, in code tags.

#3

delSMS() and myDisplay.DisplayString(tempString, 0) both look like they are operations that could be slow.

Don't call them from an ISR - during an ISR, interrupts are disabled, so if your ISR takes longer to run than it takes for a character to arrive over serial, you will lose serial data.

Set a flag in the ISR (be sure to make this global flag variable volatile), and check for that in loop and take the appropriate actions if it is set.

#4