mdbx: extract internal osal_yield() (backport).

src/atomics-ops.h

@@ -171,10 +171,8 @@ MDBX_MAYBE_UNUSED static __always_inline void atomic_yield(void) {
 #elif defined(__mips) || defined(__mips__) || defined(__mips64) || defined(__mips64__) || defined(_M_MRX000) ||        \
     defined(_MIPS_) || defined(__MWERKS__) || defined(__sgi)
   __asm__ __volatile__(".word 0x00000140");
-#elif defined(__linux__) || defined(__gnu_linux__) || defined(_UNIX03_SOURCE)
+#else
-  sched_yield();
+  osal_yield();
-#elif (defined(_GNU_SOURCE) && __GLIBC_PREREQ(2, 1)) || defined(_OPEN_THREADS)
-  pthread_yield();
 #endif
 }
 

src/coherency.c

@@ -103,15 +103,7 @@ __cold int coherency_timeout(uint64_t *timestamp, intptr_t pgno, const MDBX_env
   }
 
   osal_memory_fence(mo_AcquireRelease, true);
-#if defined(_WIN32) || defined(_WIN64)
+  osal_yield();
-  SwitchToThread();
-#elif defined(__linux__) || defined(__gnu_linux__) || defined(_UNIX03_SOURCE)
-  sched_yield();
-#elif (defined(_GNU_SOURCE) && __GLIBC_PREREQ(2, 1)) || defined(_OPEN_THREADS)
-  pthread_yield();
-#else
-  usleep(42);
-#endif
   return MDBX_RESULT_TRUE;
 }
 

src/dbi.c

@@ -172,13 +172,8 @@ int dbi_defer_release(MDBX_env *const env, defer_free_item_t *const chain) {
 #endif /* MDBX_ENABLE_DBI_LOCKFREE */
 
   ENSURE(env, osal_fastmutex_release(&env->dbi_lock) == MDBX_SUCCESS);
-  if (length > 42) {
+  if (length > 42)
-#if defined(_WIN32) || defined(_WIN64)
+    osal_yield();
-    SwitchToThread();
-#else
-    sched_yield();
-#endif /* Windows */
-  }
   while (obsolete_chain) {
     defer_free_item_t *item = obsolete_chain;
     obsolete_chain = obsolete_chain->next;

src/osal.c

@@ -2638,7 +2638,7 @@ __cold void osal_jitter(bool tiny) {
       break;
 #if defined(_WIN32) || defined(_WIN64)
     if (coin < 43 * 2 / 3)
-      SwitchToThread();
+      osal_yield();
     else {
       static HANDLE timer;
       if (!timer)
@@ -2653,7 +2653,7 @@ __cold void osal_jitter(bool tiny) {
       break;
     }
 #else
-    sched_yield();
+    osal_yield();
     if (coin > 43 * 2 / 3)
       usleep(coin);
 #endif

src/osal.h

@@ -171,6 +171,14 @@ typedef char pathchar_t;
 #define MDBX_PRIsPATH "s"
 #endif
 
+static inline bool osal_yield(void) {
+#if defined(_WIN32) || defined(_WIN64)
+  return SleepEx(0, true) == WAIT_IO_COMPLETION;
+#else
+  return sched_yield() != 0;
+#endif
+}
+
 typedef struct osal_mmap {
   union {
     void *base;

test/osal-unix.c++

@@ -572,11 +572,6 @@ int osal_actor_poll(mdbx_pid_t &pid, unsigned timeout) {
   return sigbreak ? EINTR : 0 /* timeout */;
 }
 
-void osal_yield(void) {
-  if (sched_yield())
-    failure_perror("sched_yield()", errno);
-}
-
 void osal_udelay(size_t us) {
   chrono::time until, now = chrono::now_monotonic();
   until.fixedpoint = now.fixedpoint + chrono::from_us(us).fixedpoint;

test/osal-windows.c++

@@ -401,8 +401,6 @@ int osal_actor_poll(mdbx_pid_t &pid, unsigned timeout) {
   }
 }
 
-void osal_yield(void) { SwitchToThread(); }
-
 void osal_udelay(size_t us) {
   chrono::time until, now = chrono::now_monotonic();
   until.fixedpoint = now.fixedpoint + chrono::from_us(us).fixedpoint;

test/osal.h++

@@ -20,7 +20,6 @@ bool osal_multiactor_mode(void);
 
 int osal_delay(unsigned seconds);
 void osal_udelay(size_t us);
-void osal_yield(void);
 bool osal_istty(int fd);
 std::string osal_tempdir(void);