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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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 nsUpdateMutex_h_
#define nsUpdateMutex_h_
#include "nsIUpdateService.h"
#include "nsProfileLock.h"
#include "mozilla/StaticMutex.h"
/**
* A primitive object type suitable for acquiring the update mutex. It is
* composed of two parts:
* - a nsProfileLock taken on the update directory, to ensure that if two
* instances running from the same application path try to acquire the
* update mutex simultaneously, only one of them succeeds;
* - a StaticMutex, to ensure that even within the same instance of the
* application, it is never possible to successfully acquire two
* UpdateMutexImpl objects simultaneously.
*
* While the second part is not strictly required, it makes reasoning about
* these objects easier, and it helps us simulate an acquisition coming from
* another instance in tests.
*
* Contrary to a nsIUpdateMutex object, an UpdateMutexImpl object does not
* keep track of whether it is currently locked or unlocked. Therefore, it is
* the responsibility of the caller to guarantee the following:
* - a call to Unlock() must only occur after a matching successful call to
* TryLock();
* - no second call to TryLock() should ever occur after a successful first
* call to TryLock(), unless a call to Unlock() occured in the middle.
*/
class MOZ_CAPABILITY("mutex") UpdateMutexImpl {
public:
[[nodiscard]] bool TryLock() MOZ_TRY_ACQUIRE(true);
void Unlock() MOZ_CAPABILITY_RELEASE();
private:
static mozilla::StaticMutex sInProcessMutex;
nsProfileLock mCrossProcessLock;
};
/**
* An XPCOM wrapper for the UpdateMutexImpl primitive type, achieving the same
* goals but through a safe XPCOM-compatible nsIUpdateMutex interface.
*
* Contrary to UpdateMutexImpl objects, nsUpdateMutex objects track whether
* they are currently locked or unlocked. It is therefore always safe to call
* TryLock() or Unlock() on a nsUpdateMutex object.
*
* See nsIUpdateMutex in nsUpdateService.idl for more details.
*/
class nsUpdateMutex final : public nsIUpdateMutex {
public:
explicit nsUpdateMutex() = default;
NS_DECL_THREADSAFE_ISUPPORTS
NS_DECL_NSIUPDATEMUTEX
private:
UpdateMutexImpl mUpdateMutexImpl;
bool mIsLocked{};
virtual ~nsUpdateMutex() {
if (mIsLocked) {
Unlock();
}
}
};
#endif // nsUpdateMutex_h_
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