зеркало из https://github.com/mozilla/gecko-dev.git
85 строки
4.4 KiB
C++
85 строки
4.4 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef MULTIINSTANCELOCK_H
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#define MULTIINSTANCELOCK_H
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#ifdef XP_WIN
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# include <windows.h>
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#endif
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// These functions manage "multi-instance locks", which are a type of lock
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// specifically designed to allow instances of an application, process, or other
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// task to detect when other instances relevant to them are running. Each
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// instance opens a lock and holds it for the duration of the task of interest
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// (which may be the lifetime of the process, or a shorter period). Then while
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// the lock is open, it can be used to check whether any other instances of the
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// same task are currently running out of the same copy of the binary, in the
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// context of any OS user. A process can open any number of locks, so long as
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// they use different names. It is necessary for the process to have permission
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// to create files in /tmp/ on POSIX systems or ProgramData\[vendor]\ on
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// Windows, so this mechanism may not work for sandboxed processes.
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// The implementation is based on file locking. An empty file is created in a
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// systemwide (not per-user) location, and a shared (read) lock is taken on that
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// file; the value that OpenMultiInstanceLock() returns is the file
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// handle/descriptor. When you call IsOtherInstanceRunning(), it will attempt to
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// convert that shared lock into an exclusive (write) lock. If that operation
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// would succeed, it means that there must not be any other shared locks
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// currently taken on that file, so we know there are no other instances
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// running. This is a more complex design than most file locks or most other
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// concurrency mechanisms, but it is necessary for this use case because of the
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// requirement that an instance must be able to detect other instances that were
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// started later than it was. If, say, a mutex were used, or another kind of
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// exclusive lock, then the first instance that tried to take it would succeed,
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// and be unable to tell that another instance had tried to take it later and
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// failed. This mechanism allows any number of instances started at any time in
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// relation to one another to always be able to detect that the others exist
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// (although it does not allow you to know how many others exist). The lock is
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// guaranteed to be released if the process holding it crashes or is exec'd into
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// something else, because the file is closed when that happens. The file itself
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// is not necessarily always deleted on POSIX, because it isn't possible (within
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// reason) to guarantee that unlink() is called, but the file is empty and
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// created in the /tmp directory, so should not be a serious problem.
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namespace mozilla {
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#ifdef XP_WIN
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using MultiInstLockHandle = HANDLE;
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# define MULTI_INSTANCE_LOCK_HANDLE_ERROR INVALID_HANDLE_VALUE
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#else
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using MultiInstLockHandle = int;
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# define MULTI_INSTANCE_LOCK_HANDLE_ERROR -1
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#endif
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/*
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* nameToken should be a string very briefly naming the lock you are creating
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* creating, and it should be unique except for across multiple instances of the
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* same application. The vendor name is included in the generated path, so it
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* doesn't need to be present in your supplied name. Try to keep this name sort
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* of short, ideally under about 64 characters, because creating the lock will
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* fail if the final path string (the token + the path hash + the vendor name)
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* is longer than the platform's maximum path and/or path component length.
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*
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* installPath should be the path to the directory containing the application,
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* which will be used to form a path specific to that installation.
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*
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* Returns MULTI_INSTANCE_LOCK_HANDLE_ERROR upon failure, or a handle which can
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* later be passed to the other functions declared here upon success.
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*/
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MultiInstLockHandle OpenMultiInstanceLock(const char* nameToken,
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const char16_t* installPath);
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void ReleaseMultiInstanceLock(MultiInstLockHandle lock);
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// aResult will be set to true if another instance *was* found, false if not.
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// Return value is true on success, false on error (and aResult won't be set).
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bool IsOtherInstanceRunning(MultiInstLockHandle lock, bool* aResult);
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}; // namespace mozilla
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#endif // MULTIINSTANCELOCK_H
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