[wasm] Use std::shared_mutex instead of base::SharedMutex

base::SharedMutex was implemented as an exclusive lock on Mac, because
of an OS issue on Mac (see https://crbug.com/v8/12037).
https://crrev.com/c/3855361 then introduced a custom implementation on
Mac, which caused performance regressions (see
https://crbug.com/1358856).

Since we rely on C++17 now, we can instead just use {std::shared_mutex},
which does not seem to have the deadlock issue of {pthread_rwlock_t}.
As a smoke test (and to check whether this actually fixes the
performance regressions), only switch one mutex in Wasm compilation to
std::shared_mutex. If this CL looks good, then other places can be
switched over as well.

R=ishell@chromium.org

Bug: chromium:1358856, v8:13256
Change-Id: Ia56efcb7747f191cc3ed7a381096c8f57142aff8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3868954
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82916}

src/wasm/module-compiler.cc

@@ -6,6 +6,7 @@
 
 #include <algorithm>
 #include <queue>
+#include <shared_mutex>
 
 #include "src/api/api-inl.h"
 #include "src/base/enum-set.h"
@@ -136,14 +137,14 @@ class CompilationUnitQueues {
   Queue* GetQueueForTask(int task_id) {
     int required_queues = task_id + 1;
     {
-      base::SharedMutexGuard<base::kShared> queues_guard(&queues_mutex_);
+      std::shared_lock<std::shared_mutex> queues_guard{queues_mutex_};
       if (V8_LIKELY(static_cast<int>(queues_.size()) >= required_queues)) {
         return queues_[task_id].get();
       }
     }
 
     // Otherwise increase the number of queues.
-    base::SharedMutexGuard<base::kExclusive> queues_guard(&queues_mutex_);
+    std::unique_lock<std::shared_mutex> queues_guard{queues_mutex_};
     int num_queues = static_cast<int>(queues_.size());
     while (num_queues < required_queues) {
       int steal_from = num_queues + 1;
@@ -198,7 +199,7 @@ class CompilationUnitQueues {
     QueueImpl* queue;
     {
       int queue_to_add = next_queue_to_add.load(std::memory_order_relaxed);
-      base::SharedMutexGuard<base::kShared> queues_guard(&queues_mutex_);
+      std::shared_lock<std::shared_mutex> queues_guard{queues_mutex_};
       while (!next_queue_to_add.compare_exchange_weak(
           queue_to_add, next_task_id(queue_to_add, queues_.size()),
           std::memory_order_relaxed)) {
@@ -232,7 +233,7 @@ class CompilationUnitQueues {
   }
 
   void AddTopTierPriorityUnit(WasmCompilationUnit unit, size_t priority) {
-    base::SharedMutexGuard<base::kShared> queues_guard(&queues_mutex_);
+    std::shared_lock<std::shared_mutex> queues_guard{queues_mutex_};
     // Add to the individual queues in a round-robin fashion. No special care is
     // taken to balance them; they will be balanced by work stealing.
     // Priorities should only be seen as a hint here; without balancing, we
@@ -380,7 +381,7 @@ class CompilationUnitQueues {
     // Try to steal from all other queues. If this succeeds, return one of the
     // stolen units.
     {
-      base::SharedMutexGuard<base::kShared> guard(&queues_mutex_);
+      std::shared_lock<std::shared_mutex> guard{queues_mutex_};
       for (size_t steal_trials = 0; steal_trials < queues_.size();
            ++steal_trials, ++steal_task_id) {
         if (steal_task_id >= static_cast<int>(queues_.size())) {
@@ -437,7 +438,7 @@ class CompilationUnitQueues {
     // Try to steal from all other queues. If this succeeds, return one of the
     // stolen units.
     {
-      base::SharedMutexGuard<base::kShared> guard(&queues_mutex_);
+      std::shared_lock<std::shared_mutex> guard{queues_mutex_};
       for (size_t steal_trials = 0; steal_trials < queues_.size();
            ++steal_trials, ++steal_task_id) {
         if (steal_task_id >= static_cast<int>(queues_.size())) {
@@ -512,7 +513,7 @@ class CompilationUnitQueues {
   }
 
   // {queues_mutex_} protectes {queues_};
-  base::SharedMutex queues_mutex_;
+  std::shared_mutex queues_mutex_;
   std::vector<std::unique_ptr<QueueImpl>> queues_;
 
   const int num_declared_functions_;