LibThreading: Add RWLock and RWLockedProtected

Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/5cc90f848f
Pull-request: https://github.com/SerenityOS/serenity/pull/24313
Reviewed-by: https://github.com/Zaggy1024

Userland/Libraries/LibThreading/RWLock.h

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2024, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Assertions.h>
+#include <AK/Noncopyable.h>
+#include <AK/Types.h>
+#include <pthread.h>
+
+namespace Threading {
+
+class RWLock {
+    AK_MAKE_NONCOPYABLE(RWLock);
+    AK_MAKE_NONMOVABLE(RWLock);
+
+public:
+    RWLock()
+    {
+        pthread_rwlock_init(&m_rwlock, nullptr);
+    }
+
+    ~RWLock()
+    {
+        VERIFY(!m_write_locked);
+        pthread_rwlock_destroy(&m_rwlock);
+    }
+
+    void lock_read();
+    void lock_write();
+
+    void unlock();
+
+private:
+    pthread_rwlock_t m_rwlock;
+    bool m_write_locked { false };
+    bool m_read_locked_with_write_lock { false };
+};
+
+enum class LockMode {
+    Read,
+    Write,
+};
+template<LockMode mode>
+class RWLockLocker {
+    AK_MAKE_NONCOPYABLE(RWLockLocker);
+    AK_MAKE_NONMOVABLE(RWLockLocker);
+
+public:
+    ALWAYS_INLINE explicit RWLockLocker(RWLock& l)
+        : m_lock(l)
+    {
+        lock();
+    }
+
+    ALWAYS_INLINE ~RWLockLocker()
+    {
+        unlock();
+    }
+
+    ALWAYS_INLINE void unlock()
+    {
+        m_lock.unlock();
+    }
+
+    ALWAYS_INLINE void lock()
+    {
+        if constexpr (mode == LockMode::Read)
+            m_lock.lock_read();
+        else
+            m_lock.lock_write();
+    }
+
+private:
+    RWLock& m_lock;
+};
+
+ALWAYS_INLINE void RWLock::lock_read()
+{
+    auto rc = pthread_rwlock_rdlock(&m_rwlock);
+    if (rc == EDEADLK) {
+        // We're already holding the write lock, so we can just return.
+        m_read_locked_with_write_lock = true;
+    } else {
+        VERIFY(rc == 0);
+    }
+}
+
+ALWAYS_INLINE void RWLock::lock_write()
+{
+    auto rc = pthread_rwlock_wrlock(&m_rwlock);
+    VERIFY(rc == 0);
+    m_write_locked = true;
+}
+
+ALWAYS_INLINE void RWLock::unlock()
+{
+    m_write_locked = false;
+    auto needs_unlock = !m_read_locked_with_write_lock;
+    m_read_locked_with_write_lock = false;
+    if (needs_unlock)
+        pthread_rwlock_unlock(&m_rwlock);
+}
+
+}

Userland/Libraries/LibThreading/RWLockProtected.h

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2024, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Concepts.h>
+#include <AK/Noncopyable.h>
+#include <LibThreading/RWLock.h>
+
+namespace Threading {
+
+template<typename T>
+class RWLockProtected {
+    AK_MAKE_NONCOPYABLE(RWLockProtected);
+    AK_MAKE_NONMOVABLE(RWLockProtected);
+
+public:
+    using ProtectedType = T;
+
+    ALWAYS_INLINE RWLockProtected() = default;
+    ALWAYS_INLINE RWLockProtected(T&& value)
+        : m_value(move(value))
+    {
+    }
+    ALWAYS_INLINE explicit RWLockProtected(T& value)
+        : m_value(value)
+    {
+    }
+
+    template<typename Callback>
+    requires(requires { declval<Callback>()(declval<T const&>()); })
+    decltype(auto) with_read_locked(Callback callback) const
+    {
+        auto lock = this->lock_read();
+        return callback(m_value);
+    }
+
+    template<typename Callback>
+    decltype(auto) with_write_locked(Callback callback)
+    {
+        auto lock = this->lock_write();
+        return callback(m_value);
+    }
+
+    template<VoidFunction<T> Callback>
+    void for_each_locked(Callback callback)
+    {
+        with_read_locked([&](auto const& value) {
+            for (auto& item : value)
+                callback(item);
+        });
+    }
+
+private:
+    [[nodiscard]] ALWAYS_INLINE RWLockLocker<LockMode::Read> lock_read() const
+    {
+        return RWLockLocker<LockMode::Read> { m_lock };
+    }
+
+    [[nodiscard]] ALWAYS_INLINE RWLockLocker<LockMode::Write> lock_write()
+    {
+        return RWLockLocker<LockMode::Write> { m_lock };
+    }
+
+    T m_value;
+    mutable RWLock m_lock {};
+};
+
+}