Introduce no spin policy for SharedMutex

Summary:
In some cases we known there is no need to spin at all for various reasons.
Introduce `PolicyNoSpin` and `SharedMutexWritePriorityNoSpin` alias, so we can
reuse this policy.

Reviewed By: ot

Differential Revision: D53265542

fbshipit-source-id: 60fbd807827480da494f62d5ad726c5760420856

folly/SharedMutex.h

@@ -265,6 +265,9 @@ struct SharedMutexPolicyDefault {
 
 namespace shared_mutex_detail {
 
+struct PolicyNoSpin : SharedMutexPolicyDefault {
+  static constexpr uint64_t max_spin_cycles = 0;
+};
 struct PolicyTracked : SharedMutexPolicyDefault {
   static constexpr bool track_thread_id = true;
 };
@@ -1616,6 +1619,11 @@ class SharedMutexImpl : std::conditional_t<
 using SharedMutexReadPriority = SharedMutexImpl<true>;
 using SharedMutexWritePriority = SharedMutexImpl<false>;
 using SharedMutex = SharedMutexWritePriority;
+using SharedMutexNoSpin = SharedMutexImpl<
+    false,
+    void,
+    std::atomic,
+    shared_mutex_detail::PolicyNoSpin>;
 using SharedMutexTracked = SharedMutexImpl<
     false,
     void,

folly/test/SharedMutexTest.cpp

@@ -98,6 +98,7 @@ void runBasicTest() {
 TEST(SharedMutex, basic) {
   runBasicTest<SharedMutexReadPriority>();
   runBasicTest<SharedMutexWritePriority>();
+  runBasicTest<SharedMutexNoSpin>();
   runBasicTest<SharedMutexSuppressTSAN>();
   runBasicTest<SharedMutexTracked>();
 }
@@ -181,6 +182,7 @@ void runBasicHoldersTest() {
 TEST(SharedMutex, basicHolders) {
   runBasicHoldersTest<SharedMutexReadPriority>();
   runBasicHoldersTest<SharedMutexWritePriority>();
+  runBasicHoldersTest<SharedMutexNoSpin>();
   runBasicHoldersTest<SharedMutexSuppressTSAN>();
   runBasicHoldersTest<SharedMutexTracked>();
 }
@@ -209,6 +211,7 @@ TEST(SharedMutex, manyReadLocksWithTokens) {
   SKIP_IF(folly::kIsSanitizeThread);
   runManyReadLocksTestWithTokens<SharedMutexReadPriority>();
   runManyReadLocksTestWithTokens<SharedMutexWritePriority>();
+  runManyReadLocksTestWithTokens<SharedMutexNoSpin>();
   runManyReadLocksTestWithTokens<SharedMutexSuppressTSAN>();
   runManyReadLocksTestWithTokens<SharedMutexTracked>();
 }
@@ -235,6 +238,7 @@ TEST(SharedMutex, manyReadLocksWithoutTokens) {
   SKIP_IF(folly::kIsSanitizeThread);
   runManyReadLocksTestWithoutTokens<SharedMutexReadPriority>();
   runManyReadLocksTestWithoutTokens<SharedMutexWritePriority>();
+  runManyReadLocksTestWithoutTokens<SharedMutexNoSpin>();
   runManyReadLocksTestWithoutTokens<SharedMutexSuppressTSAN>();
   runManyReadLocksTestWithoutTokens<SharedMutexTracked>();
 }
@@ -266,6 +270,7 @@ void runTimeoutInPastTest() {
 TEST(SharedMutex, timeoutInPast) {
   runTimeoutInPastTest<SharedMutexReadPriority>();
   runTimeoutInPastTest<SharedMutexWritePriority>();
+  runTimeoutInPastTest<SharedMutexNoSpin>();
   runTimeoutInPastTest<SharedMutexSuppressTSAN>();
   runTimeoutInPastTest<SharedMutexTracked>();
 }
@@ -354,6 +359,7 @@ void runFailingTryTimeoutTest() {
 TEST(SharedMutex, failingTryTimeout) {
   runFailingTryTimeoutTest<SharedMutexReadPriority>();
   runFailingTryTimeoutTest<SharedMutexWritePriority>();
+  runFailingTryTimeoutTest<SharedMutexNoSpin>();
   runFailingTryTimeoutTest<SharedMutexSuppressTSAN>();
   runFailingTryTimeoutTest<SharedMutexTracked>();
 }
@@ -399,6 +405,7 @@ void runBasicUpgradeTest() {
 TEST(SharedMutex, basicUpgradeTests) {
   runBasicUpgradeTest<SharedMutexReadPriority>();
   runBasicUpgradeTest<SharedMutexWritePriority>();
+  runBasicUpgradeTest<SharedMutexNoSpin>();
   runBasicUpgradeTest<SharedMutexSuppressTSAN>();
   runBasicUpgradeTest<SharedMutexTracked>();
 }