start moving algorithm in

userland/cpp/atomic.cpp

@@ -1,98 +0,0 @@
-// https://cirosantilli.com/linux-kernel-module-cheat#cpp-multithreading
-//
-// The non-atomic counters have undefined values which get printed:
-// they are extremely likely to be less than the correct value due to
-// race conditions on the data read and update of the ++.
-//
-// The atomic counters have defined values, and are asserted
-//
-// Atomic operations are more restricted than mutex as they can
-// only protect a few operations on integers.
-//
-// But when they can be used, they can be much more efficient than mutees.
-//
-// On GCC 4.8 x86-64, using atomic offered a 5x peformance improvement
-// over the same program with mutexes.
-
-#if __cplusplus >= 201103L
-#include <atomic>
-#include <cassert>
-#include <iostream>
-#include <thread>
-#include <vector>
-
-std::atomic_ulong my_atomic_ulong(0);
-unsigned long my_non_atomic_ulong = 0;
-#if defined(__x86_64__) || defined(__aarch64__)
-unsigned long my_arch_atomic_ulong = 0;
-unsigned long my_arch_non_atomic_ulong = 0;
-#endif
-size_t niters;
-
-void threadMain() {
-    for (size_t i = 0; i < niters; ++i) {
-        my_atomic_ulong++;
-        my_non_atomic_ulong++;
-#if defined(__x86_64__)
-        __asm__ __volatile__ (
-            "incq %0;"
-            : "+m" (my_arch_non_atomic_ulong)
-            :
-            :
-        );
-        // https://cirosantilli.com/linux-kernel-module-cheat#x86-lock-prefix
-        __asm__ __volatile__ (
-            "lock;"
-            "incq %0;"
-            : "+m" (my_arch_atomic_ulong)
-            :
-            :
-        );
-#elif defined(__aarch64__)
-        __asm__ __volatile__ (
-            "add %0, %0, 1;"
-            : "+r" (my_arch_non_atomic_ulong)
-            :
-            :
-        );
-        // https://cirosantilli.com/linux-kernel-module-cheat#arm-lse
-        __asm__ __volatile__ (
-            "ldadd %[inc], xzr, [%[addr]];"
-            : "=m" (my_arch_atomic_ulong)
-            : [inc] "r" (1),
-              [addr] "r" (&my_arch_atomic_ulong)
-            :
-        );
-#endif
-    }
-}
-#endif
-
-int main(int argc, char **argv) {
-#if __cplusplus >= 201103L
-    size_t nthreads;
-    if (argc > 1) {
-        nthreads = std::stoull(argv[1], NULL, 0);
-    } else {
-        nthreads = 2;
-    }
-    if (argc > 2) {
-        niters = std::stoull(argv[2], NULL, 0);
-    } else {
-        niters = 10;
-    }
-    std::vector<std::thread> threads(nthreads);
-    for (size_t i = 0; i < nthreads; ++i)
-        threads[i] = std::thread(threadMain);
-    for (size_t i = 0; i < nthreads; ++i)
-        threads[i].join();
-    assert(my_atomic_ulong.load() == nthreads * niters);
-    // We can also use the atomics direclty through `operator T` conversion.
-    assert(my_atomic_ulong == my_atomic_ulong.load());
-    std::cout << "my_non_atomic_ulong " << my_non_atomic_ulong << std::endl;
-#if defined(__x86_64__) || defined(__aarch64__)
-    assert(my_arch_atomic_ulong == nthreads * niters);
-    std::cout << "my_arch_non_atomic_ulong " << my_arch_non_atomic_ulong << std::endl;
-#endif
-#endif
-}