ReportingAllocator from the book Rust in Action

reporting-allocator.rs

#[global_allocator]
static ALLOCATOR: ReportingAllocator = ReportingAllocator;

struct ReportingAllocator;

unsafe impl GlobalAlloc for ReportingAllocator {
  unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
    let start = Instant::now();
    let ptr = System.alloc(layout);
    let end = Instant::now();
    let time_taken = end - start;
    let bytes_requested = layout.size();
    
    eprintln!("{}\t{}", bytes_requested, time_taken.as_nanos());
    ptr
  }
  
  unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
    System.dealloc(ptr, layout);
  }
}