Hi all,
Please help me out.
I posted my trigger please it throws the exception 

Exception Details: Update failed. First exception on row 0 with id 0035000003IGI8AAAX; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, ContactTrainerCountTrigger: execution of AfterUpdate

caused by: System.QueryException: Record Currently Unavailable: The record you are attempting to edit, or one of its related records, is currently being modified by another user. Please try again.

My trigger named "ConactTrainerCountTrigger" and the trigger code is given below:
trigger ContactTrainerCountTrigger on Contact (After insert, After delete, After undelete, After Update) {
    Set<Id> parentIdsSet = new Set<Id>();
    List<Account> accountListToUpdate = new List<Account>();
    IF(Trigger.IsAfter){
        IF(Trigger.IsInsert || Trigger.IsUndelete){
            FOR(Contact c : Trigger.new){
                if(c.AccountId!=null){   
                    parentIdsSet.add(c.AccountId);
                    
                }
            }
            System.debug('parentIdsSet' + parentIdsSet);
        }
        IF(Trigger.IsUpdate){
            FOR(Contact c : Trigger.new){
                if(c.AccountId!=null){
                    if(Trigger.oldMap.get(c.Id).Type__c != c.Type__c || Trigger.oldMap.get(c.Id).AccountId != c.AccountId){
                        parentIdsSet.add(Trigger.oldMap.get(c.Id).AccountId);
                        parentIdsSet.add(c.AccountId);
                    }
                }
            }
        }
        IF(Trigger.IsDelete){
            FOR(Contact c : Trigger.Old){
                if(c.AccountId!=null){   
                    parentIdsSet.add(c.AccountId); 
                }
            }
        }
        
          
        List<Account> accountList = new List<Account>([Select id ,Name,Trainer_Count__c, (Select id, Name From Contacts where Type__c = 'Trainer') from Account Where id in:parentIdsSet for Update]);
        System.debug('accountList' + accountList);
        FOR(Account acc : accountList){
            System.debug('acc' +acc);
            List<Contact> contactList = acc.Contacts;
            acc.Trainer_Count__c = contactList.size();
            accountListToUpdate.add(acc);
        }
        update accountListToUpdate;
 
    }
    
}