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diff --git a/mozglue/misc/WinUtils.h b/mozglue/misc/WinUtils.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_glue_MozglueUtils_h
+#define mozilla_glue_MozglueUtils_h
+
+#include <windows.h>
+
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+
+namespace mozilla {
+namespace glue {
+
+#ifdef DEBUG
+
+class MOZ_STATIC_CLASS Win32SRWLock final {
+ public:
+ // Microsoft guarantees that '0' is never a valid thread id
+ // https://docs.microsoft.com/en-ca/windows/desktop/ProcThread/thread-handles-and-identifiers
+ static const DWORD kInvalidThreadId = 0;
+
+ constexpr Win32SRWLock()
+ : mExclusiveThreadId(kInvalidThreadId), mLock(SRWLOCK_INIT) {}
+
+ ~Win32SRWLock() { MOZ_ASSERT(mExclusiveThreadId == kInvalidThreadId); }
+
+ void LockShared() {
+ MOZ_ASSERT(
+ mExclusiveThreadId != GetCurrentThreadId(),
+ "Deadlock detected - A thread attempted to acquire a shared lock on "
+ "a SRWLOCK when it already owns the exclusive lock on it.");
+
+ ::AcquireSRWLockShared(&mLock);
+ }
+
+ void UnlockShared() { ::ReleaseSRWLockShared(&mLock); }
+
+ void LockExclusive() {
+ MOZ_ASSERT(
+ mExclusiveThreadId != GetCurrentThreadId(),
+ "Deadlock detected - A thread attempted to acquire an exclusive lock "
+ "on a SRWLOCK when it already owns the exclusive lock on it.");
+
+ ::AcquireSRWLockExclusive(&mLock);
+ mExclusiveThreadId = GetCurrentThreadId();
+ }
+
+ void UnlockExclusive() {
+ MOZ_ASSERT(mExclusiveThreadId == GetCurrentThreadId());
+
+ mExclusiveThreadId = kInvalidThreadId;
+ ::ReleaseSRWLockExclusive(&mLock);
+ }
+
+ Win32SRWLock(const Win32SRWLock&) = delete;
+ Win32SRWLock(Win32SRWLock&&) = delete;
+ Win32SRWLock& operator=(const Win32SRWLock&) = delete;
+ Win32SRWLock& operator=(Win32SRWLock&&) = delete;
+
+ private:
+ // "Relaxed" memory ordering is fine. Threads will see other thread IDs
+ // appear here in some non-deterministic ordering (or not at all) and simply
+ // ignore them.
+ //
+ // But a thread will only read its own ID if it previously wrote it, and a
+ // single thread doesn't need a memory barrier to read its own write.
+
+ Atomic<DWORD, Relaxed> mExclusiveThreadId;
+ SRWLOCK mLock;
+};
+
+#else // DEBUG
+
+class MOZ_STATIC_CLASS Win32SRWLock final {
+ public:
+ constexpr Win32SRWLock() : mLock(SRWLOCK_INIT) {}
+
+ void LockShared() { ::AcquireSRWLockShared(&mLock); }
+
+ void UnlockShared() { ::ReleaseSRWLockShared(&mLock); }
+
+ void LockExclusive() { ::AcquireSRWLockExclusive(&mLock); }
+
+ void UnlockExclusive() { ::ReleaseSRWLockExclusive(&mLock); }
+
+ ~Win32SRWLock() = default;
+
+ Win32SRWLock(const Win32SRWLock&) = delete;
+ Win32SRWLock(Win32SRWLock&&) = delete;
+ Win32SRWLock& operator=(const Win32SRWLock&) = delete;
+ Win32SRWLock& operator=(Win32SRWLock&&) = delete;
+
+ private:
+ SRWLOCK mLock;
+};
+
+#endif
+
+class MOZ_RAII AutoSharedLock final {
+ public:
+ explicit AutoSharedLock(Win32SRWLock& aLock) : mLock(aLock) {
+ mLock.LockShared();
+ }
+
+ ~AutoSharedLock() { mLock.UnlockShared(); }
+
+ AutoSharedLock(const AutoSharedLock&) = delete;
+ AutoSharedLock(AutoSharedLock&&) = delete;
+ AutoSharedLock& operator=(const AutoSharedLock&) = delete;
+ AutoSharedLock& operator=(AutoSharedLock&&) = delete;
+
+ private:
+ Win32SRWLock& mLock;
+};
+
+class MOZ_RAII AutoExclusiveLock final {
+ public:
+ explicit AutoExclusiveLock(Win32SRWLock& aLock) : mLock(aLock) {
+ mLock.LockExclusive();
+ }
+
+ ~AutoExclusiveLock() { mLock.UnlockExclusive(); }
+
+ AutoExclusiveLock(const AutoExclusiveLock&) = delete;
+ AutoExclusiveLock(AutoExclusiveLock&&) = delete;
+ AutoExclusiveLock& operator=(const AutoExclusiveLock&) = delete;
+ AutoExclusiveLock& operator=(AutoExclusiveLock&&) = delete;
+
+ private:
+ Win32SRWLock& mLock;
+};
+
+} // namespace glue
+} // namespace mozilla
+
+#endif // mozilla_glue_MozglueUtils_h