[Lldb-commits] [lldb] [lldb] Use os_unfair_lock for the string pool on Darwin (PR #197851)

[Jonas Devlieghere via lldb-commits]

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@@ -15,18 +15,71 @@
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/DJB.h"
 #include "llvm/Support/FormatProviders.h"
-#include "llvm/Support/RWMutex.h"
 #include "llvm/Support/Threading.h"
 
 #include <array>
+#include <mutex>
+#include <shared_mutex>
 #include <utility>
 
 #include <cinttypes>
 #include <cstdint>
 #include <cstring>
 
+#if defined(__APPLE__)
+#include <os/lock.h>
+#endif
+
 using namespace lldb_private;
 
+namespace {
+/// Lock guarding each shard of the ConstString pool. On Apple platforms it
+/// wraps os_unfair_lock, which is significantly faster than pthread_rwlock for
+/// concurrent writes, and roughly on par for concurrent reads. On all other
+/// platforms, it wraps std::shared_mutex, preserving reader/writer concurrency.
+///
+/// The class satisfies both Lockable and SharedLockable so it composes with
+/// std::lock_guard and std::shared_lock.
+class PoolMutex {
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JDevlieghere wrote:

That would simplify things a lot. Done.

https://github.com/llvm/llvm-project/pull/197851