thread: add uv_thread_getcpu() (#3803)

Add uv_thread_getcpu() api to get the cpu number on which the calling
thread is running.

docs/src/threading.rst

@@ -119,6 +119,15 @@ Threads
 
     .. versionadded:: 1.45.0
 
+.. c:function:: int uv_thread_getcpu(void)
+
+    Gets the CPU number on which the calling thread is running.
+
+    .. note::
+        Currently only implemented on Windows, Linux and FreeBSD.
+
+    .. versionadded:: 1.45.0
+
 .. c:function:: uv_thread_t uv_thread_self(void)
 .. c:function:: int uv_thread_join(uv_thread_t *tid)
 .. c:function:: int uv_thread_equal(const uv_thread_t* t1, const uv_thread_t* t2)

include/uv.h

@@ -1802,6 +1802,7 @@ UV_EXTERN int uv_thread_setaffinity(uv_thread_t* tid,
 UV_EXTERN int uv_thread_getaffinity(uv_thread_t* tid,
                                     char* cpumask,
                                     size_t mask_size);
+UV_EXTERN int uv_thread_getcpu(void);
 UV_EXTERN uv_thread_t uv_thread_self(void);
 UV_EXTERN int uv_thread_join(uv_thread_t *tid);
 UV_EXTERN int uv_thread_equal(const uv_thread_t* t1, const uv_thread_t* t2);

src/unix/thread.c

@@ -382,6 +382,19 @@ int uv_thread_getaffinity(uv_thread_t* tid,
 }
 #endif /* defined(__linux__) || defined(UV_BSD_H) */
 
+int uv_thread_getcpu(void) {
+#if defined(__linux__) || defined(__FreeBSD__)
+  int cpu;
+
+  cpu = sched_getcpu();
+  if (cpu < 0)
+    return UV__ERR(errno);
+
+  return cpu;
+#else
+  return UV_ENOTSUP;
+#endif
+}
 
 uv_thread_t uv_thread_self(void) {
   return pthread_self();

src/win/thread.c

@@ -252,6 +252,9 @@ int uv_thread_getaffinity(uv_thread_t* tid,
   return 0;
 }
 
+int uv_thread_getcpu(void) {
+  return GetCurrentProcessorNumber();
+}
 
 uv_thread_t uv_thread_self(void) {
   uv_thread_t key;

test/test-thread-affinity.c

@@ -34,6 +34,8 @@ TEST_IMPL(thread_affinity) {
   char* cpumask;
   int ncpus;
   int r;
+  int c;
+  int i;
   uv_thread_t threads[3];
 
 #ifdef _WIN32
@@ -99,6 +101,24 @@ TEST_IMPL(thread_affinity) {
   ASSERT(cpumask[t2first + 2] == (ncpus >= 3));
   ASSERT(cpumask[t2first + 3] == 0);
 
+  c = uv_thread_getcpu();
+  ASSERT_GE(c, 0);
+
+  memset(cpumask, 0, cpumasksize);
+  cpumask[c] = 1;
+  r = uv_thread_setaffinity(&threads[0], cpumask, NULL, cpumasksize);
+  ASSERT_EQ(r, 0);
+
+  memset(cpumask, 0, cpumasksize);
+  r = uv_thread_getaffinity(&threads[0], cpumask, cpumasksize);
+  ASSERT_EQ(r, 0);
+  for (i = 0; i < cpumasksize; i++) {
+    if (i == c)
+      ASSERT_EQ(1, cpumask[i]);
+    else
+      ASSERT_EQ(0, cpumask[i]);
+  }
+
   free(cpumask);
 
   return 0;