Atomic Counters in Assembly Language

; The primary mechanism for managing state in concurrent programs is
; through shared memory. Here we'll look at using atomic operations
; for counters accessed by multiple threads.

section .data
    counter dq 0               ; 64-bit counter initialized to 0
    fmt db "ops: %llu", 10, 0  ; Format string for printf

section .text
    global main
    extern printf

main:
    push rbp
    mov rbp, rsp

    ; We'll start 50 threads that each increment the
    ; counter exactly 1000 times.
    mov rcx, 50                ; Number of threads
create_threads:
    push rcx                   ; Save loop counter
    ; Create thread (simplified, actual thread creation would be more complex)
    call increment_counter
    pop rcx                    ; Restore loop counter
    loop create_threads

    ; Wait for all threads to finish (simplified)
    ; In a real scenario, you'd use proper synchronization primitives

    ; Print the final counter value
    mov rdi, fmt
    mov rsi, [counter]
    xor rax, rax
    call printf

    ; Exit program
    xor rax, rax
    leave
    ret

increment_counter:
    ; Each thread increments the counter 1000 times
    mov rcx, 1000
increment_loop:
    lock inc qword [counter]   ; Atomic increment of the counter
    loop increment_loop
    ret

In this Assembly Language example, we’re demonstrating the concept of atomic counters. Here’s a breakdown of the code:

1. We define a 64-bit counter in the .data section, initialized to 0.

2. In the main function, we simulate creating 50 threads. Each “thread” is represented by a call to the increment_counter function.

3. The increment_counter function increments the counter 1000 times using the lock inc instruction. This instruction ensures that the increment operation is atomic, preventing race conditions when multiple threads access the counter simultaneously.

4. After all “threads” have completed, we print the final value of the counter using printf.

Note that this is a simplified example. In real assembly programming:

• Thread creation and synchronization would be more complex and depend on the specific operating system.
• You’d need to use proper thread synchronization primitives to ensure all threads complete before printing the result.
• Error handling and proper stack management would be necessary.

When you run this program, you should see output similar to:

ops: 50000

This demonstrates that the atomic operations ensured all 50,000 increments (50 threads * 1000 increments each) were correctly counted without any race conditions.

Next, we could explore other synchronization primitives in assembly language for managing shared state in concurrent programs.