multithreading - Reusing a global array in a function in a threadsafe way in C -

i want use temporary storage in function , not have reallocate @ each call. works fine single thread, how extend idea multi-threaded programs (a subject i'm familiar in abstract).

for example,

int *foo_array; int foo_array_size;//global initalises 0 void foo(int *a, int n){   int i;   if(n>foo_array_size && foo_array) free(foo_array);   if(n>foo_array_size){     foo_array=malloc(2*n*sizeof(int));     foo_array_size=2*n;   }   for(i=0;i<n;i++){     foo_array[i]=a[i];   }   for(i=0;i<n;i++){     a[i]=foo_array[i];   } } 

as understand it, foo_array points same place in memory every thread, if foo() called @ same time in 2 threads, end unexpected behaviour (correct?).

so how i, @ abstract level, perhaps, ensure foo_array points different memory use in each thread?

you don't thread library using. c11 thread library has qualifier _thread_local creates variable has different incarnation per thread.

if don't have c11 threads, compiler extensions may provide similar feature. e.g gcc has __thread.

according thread library using there may set of functions simulate such thing. c11 threads have tss_t type (thread specific storage) , functions tss_create etc deal them.