1 files changed, 18 insertions, 13 deletions
diff --git a/test/core/util/port_isolated_runtime_environment.cc b/test/core/util/port_isolated_runtime_environment.cc
index ff8342ff4a..1f678c08e5 100644
--- a/test/core/util/port_isolated_runtime_environment.cc
+++ b/test/core/util/port_isolated_runtime_environment.cc
@@ -16,9 +16,12 @@
  *
  */
 
-/* When running tests on remote machines, the framework takes a round-robin pick
- * of a port within certain range. There is no need to recycle ports.
+/* When individual tests run in an isolated runtime environment (e.g. each test
+ * runs in a separate container) the framework takes a round-robin pick of a
+ * port within certain range. There is no need to recycle ports.
  */
+#include <grpc/support/atm.h>
+#include <grpc/support/log.h>
 #include <grpc/support/time.h>
 #include <stdlib.h>
 #include "src/core/lib/iomgr/port.h"
@@ -27,23 +30,25 @@
 
 #include "test/core/util/port.h"
 
-#define MIN_PORT 49152
-#define MAX_PORT 65536
+#define MIN_PORT 1025
+#define MAX_PORT 32766
 
-int get_random_starting_port() {
+static int get_random_port_offset() {
   srand(gpr_now(GPR_CLOCK_REALTIME).tv_nsec);
-  return rand() % (MAX_PORT - MIN_PORT + 1) + MIN_PORT;
+  double rnd = static_cast<double>(rand()) /
+               (static_cast<double>(RAND_MAX) + 1.0);  // values from [0,1)
+  return static_cast<int>(rnd * (MAX_PORT - MIN_PORT + 1));
 }
 
-static int s_allocated_port = get_random_starting_port();
+static int s_initial_offset = get_random_port_offset();
+static gpr_atm s_pick_counter = 0;
 
 int grpc_pick_unused_port_or_die(void) {
-  int allocated_port = s_allocated_port++;
-  if (s_allocated_port == MAX_PORT) {
-    s_allocated_port = MIN_PORT;
-  }
-
-  return allocated_port;
+  int orig_counter_val =
+      static_cast<int>(gpr_atm_full_fetch_add(&s_pick_counter, 1));
+  GPR_ASSERT(orig_counter_val < (MAX_PORT - MIN_PORT + 1));
+  return MIN_PORT +
+         (s_initial_offset + orig_counter_val) % (MAX_PORT - MIN_PORT + 1);
 }
 
 void grpc_recycle_unused_port(int port) { (void)port; }