c++ - Is my function thread-safe and reentrant? -

i have function called 2 threads each having local copy of vector. assumption since each thread has different vector function below thread-safe.
below function thread-safe , reentrant?

int partition(int high, int low, int pivot, std::vector<int>& arr) {     int j = low;     (int = low ; <= high ; i++)     {         if (arr[i] <= pivot)         {              swap(i , j++ , arr);          }     }     return arr.size() - j; }  void swap(int fromindex , int toindex , std::vector<int> &arr) {     arr[fromindex] = arr[fromindex]^arr[toindex];     arr[toindex] = arr[fromindex]^arr[toindex];     arr[fromindex] = arr[fromindex]^arr[toindex]; } 

the function not thread-safe, because possible pass same vector different threads.

however, possible write thread-safe code using non-thread-safe functions if synchronization outside of these functions. i.e. if calling code takes care same vector never passed function @ same time, the calling code thread-safe.

about being re-entrant, wikipedia has following say:

in computing, computer program or subroutine called reentrant if can interrupted in middle of execution , safely called again ("re-entered") before previous invocations complete execution. interruption caused internal action such jump or call, or external action such hardware interrupt or signal. once reentered invocation completes, previous invocations resume correct execution.

i emphasized last part in definition, because obviously, function not thread-safe may not execute correctly , therefore cannot reentrant definition.