1 files changed, 12 insertions, 6 deletions
diff --git a/libc/src/stdlib/rand.cpp b/libc/src/stdlib/rand.cpp
index ad543b4048a9..ff3875c2f695 100644
--- a/libc/src/stdlib/rand.cpp
+++ b/libc/src/stdlib/rand.cpp
@@ -8,6 +8,7 @@
 
 #include "src/stdlib/rand.h"
 #include "src/__support/common.h"
+#include "src/__support/threads/sleep.h"
 #include "src/stdlib/rand_util.h"
 
 namespace LIBC_NAMESPACE {
@@ -15,12 +16,17 @@ namespace LIBC_NAMESPACE {
 // An implementation of the xorshift64star pseudo random number generator. This
 // is a good general purpose generator for most non-cryptographics applications.
 LLVM_LIBC_FUNCTION(int, rand, (void)) {
-  unsigned long x = rand_next;
-  x ^= x >> 12;
-  x ^= x << 25;
-  x ^= x >> 27;
-  rand_next = x;
-  return static_cast<int>((x * 0x2545F4914F6CDD1Dul) >> 32) & RAND_MAX;
+  unsigned long orig = rand_next.load(cpp::MemoryOrder::RELAXED);
+  for (;;) {
+    unsigned long x = orig;
+    x ^= x >> 12;
+    x ^= x << 25;
+    x ^= x >> 27;
+    if (rand_next.compare_exchange_strong(orig, x, cpp::MemoryOrder::ACQUIRE,
+                                          cpp::MemoryOrder::RELAXED))
+      return static_cast<int>((x * 0x2545F4914F6CDD1Dul) >> 32) & RAND_MAX;
+    sleep_briefly();
+  }
 }
 
 } // namespace LIBC_NAMESPACE