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256 lines
8.4 KiB
C++
256 lines
8.4 KiB
C++
/* 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 mozilla_IOInterposer_h
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#define mozilla_IOInterposer_h
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#include "mozilla/Attributes.h"
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#include "mozilla/TimeStamp.h"
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#include "mozilla/XPCOM.h"
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namespace mozilla {
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/**
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* Interface for I/O interposer observers. This is separate from the
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* IOInterposer because we have multiple uses for these observations.
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*/
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class IOInterposeObserver
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{
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public:
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enum Operation
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{
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OpNone = 0,
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OpCreateOrOpen = (1 << 0),
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OpRead = (1 << 1),
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OpWrite = (1 << 2),
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OpFSync = (1 << 3),
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OpStat = (1 << 4),
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OpClose = (1 << 5),
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OpWriteFSync = (OpWrite | OpFSync),
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OpAll = (OpCreateOrOpen | OpRead | OpWrite | OpFSync | OpStat | OpClose)
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};
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/** A representation of an I/O observation */
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class Observation
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{
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protected:
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Observation()
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{
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}
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public:
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Observation(Operation aOperation, const TimeStamp& aStart,
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const TimeStamp& aEnd, const char* aReference)
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: mOperation(aOperation), mStart(aStart), mEnd(aEnd),
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mReference(aReference)
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{
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}
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/**
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* Operation observed, this is either OpRead, OpWrite or OpFSync,
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* combinations of these flags are only used when registering observers.
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*/
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Operation ObservedOperation() const
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{
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return mOperation;
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}
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/** Time at which the I/O operation was started */
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TimeStamp Start() const
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{
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return mStart;
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}
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/**
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* Time at which the I/O operation ended, for asynchronous methods this is
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* the time at which the call initiating the asynchronous request returned.
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*/
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TimeStamp End() const
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{
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return mEnd;
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}
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/**
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* Duration of the operation, for asynchronous I/O methods this is the
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* duration of the call initiating the asynchronous request.
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*/
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TimeDuration Duration() const
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{
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return mEnd - mStart;
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}
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/**
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* IO reference, function name or name of component (sqlite) that did IO
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* this is in addition the generic operation. This attribute may be platform
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* specific, but should only take a finite number of distinct values.
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* E.g. sqlite-commit, CreateFile, NtReadFile, fread, fsync, mmap, etc.
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* I.e. typically the platform specific function that did the IO.
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*/
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const char* Reference() const
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{
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return mReference;
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}
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/** Request filename associated with the I/O operation, null if unknown */
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virtual const char* Filename()
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{
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return nullptr;
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}
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virtual ~Observation()
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{
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}
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protected:
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Operation mOperation;
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TimeStamp mStart;
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TimeStamp mEnd;
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const char* mReference;
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};
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/**
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* Invoked whenever an implementation of the IOInterposeObserver should
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* observe aObservation. Implement this and do your thing...
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* But do consider if it is wise to use IO functions in this method, they are
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* likely to cause recursion :)
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* At least, see PoisonIOInterposer.h and register your handle as a debug file
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* even, if you don't initialize the poison IO interposer, someone else might.
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*
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* Remark: Observations may occur on any thread.
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*/
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virtual void Observe(Observation& aObservation) = 0;
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virtual ~IOInterposeObserver()
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{
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}
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};
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#ifdef MOZ_ENABLE_PROFILER_SPS
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/**
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* Class offering the public static IOInterposer API.
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*
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* This class is responsible for ensuring that events are routed to the
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* appropriate observers. Methods Init() and Clear() should only be called from
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* the main-thread at startup and shutdown, respectively.
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*
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* Remark: Instances of this class will never be created, you should consider it
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* to be a namespace containing static functions. The class is created to
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* facilitate to a private static instance variable sObservedOperations.
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* As we want to access this from an inline static methods, we have to do this
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* trick.
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*/
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class IOInterposer MOZ_FINAL
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{
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// Track whether or not a given type of observation is being observed
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static IOInterposeObserver::Operation sObservedOperations;
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// No instance of class should be created, they'd be empty anyway.
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IOInterposer();
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public:
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/**
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* This function must be called from the main-thread when no other threads are
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* running before any of the other methods on this class may be used.
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*
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* IO reports can however, safely assume that IsObservedOperation() will
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* return false, until the IOInterposer is initialized.
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*
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* Remark, it's safe to call this method multiple times, so just call it when
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* you to utilize IO interposing.
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*/
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static void Init();
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/**
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* This function must be called from the main thread, and furthermore
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* it must be called when no other threads are executing. Effectively
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* restricting us to calling it only during shutdown.
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*
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* Callers should take care that no other consumers are subscribed to events,
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* as these events will stop when this function is called.
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*
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* In practice, we don't use this method, as the IOInterposer is used for
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* late-write checks.
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*/
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static void Clear();
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/**
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* Report IO to registered observers.
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* Notice that the reported operation must be either OpRead, OpWrite or
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* OpFSync. You are not allowed to report an observation with OpWriteFSync or
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* OpAll, these are just auxiliary values for use with Register().
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*
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* If the IO call you're reporting does multiple things, write and fsync, you
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* can choose to call Report() twice once with write and once with FSync. You
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* may not call Report() with OpWriteFSync! The Observation::mOperation
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* attribute is meant to be generic, not perfect.
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*
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* Notice that there is no reason to report an observation with an operation
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* which is not being observed. Use IsObservedOperation() to check if the
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* operation you are about to report is being observed. This is especially
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* important if you are constructing expensive observations containing
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* filename and full-path.
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*
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* Remark: Init() must be called before any IO is reported. But
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* IsObservedOperation() will return false until Init() is called.
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*/
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static void Report(IOInterposeObserver::Observation& aObservation);
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/**
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* Return whether or not an operation is observed. Reporters should not
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* report operations that are not being observed by anybody. This mechanism
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* allows us to not report IO when no observers are registered.
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*/
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static inline bool IsObservedOperation(IOInterposeObserver::Operation aOp) {
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// The quick reader may observe that no locks are being employed here,
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// hence, the result of the operations is truly undefined. However, most
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// computers will usually return either true or false, which is good enough.
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// If we occasionally report more or less IO than is being observed than
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// that is not a problem.
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return (sObservedOperations & aOp);
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}
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/**
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* Register IOInterposeObserver, the observer object will receive all
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* observations for the given operation aOp.
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*
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* Remark: Init() must be called before observers are registered.
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*/
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static void Register(IOInterposeObserver::Operation aOp,
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IOInterposeObserver* aObserver);
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/**
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* Unregister an IOInterposeObserver for a given operation
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* Remark: It is always safe to unregister for all operations, even if yoú
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* didn't register for them all.
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* I.e. IOInterposer::Unregister(IOInterposeObserver::OpAll, aObserver)
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*
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* Remark: Init() must be called before observers are unregistered
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*/
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static void Unregister(IOInterposeObserver::Operation aOp,
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IOInterposeObserver* aObserver);
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};
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#else /* MOZ_ENABLE_PROFILER_SPS */
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class IOInterposer MOZ_FINAL
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{
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IOInterposer();
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public:
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static inline void Init() {}
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static inline void Clear() {}
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static inline void Report(IOInterposeObserver::Observation& aOb) {}
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static inline void Register(IOInterposeObserver::Operation aOp,
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IOInterposeObserver* aObserver) {}
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static inline void Unregister(IOInterposeObserver::Operation aOp,
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IOInterposeObserver* aObserver) {}
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static inline bool IsObservedOperation(IOInterposeObserver::Operation aOp) {
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return false;
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}
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};
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#endif /* MOZ_ENABLE_PROFILER_SPS */
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} // namespace mozilla
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#endif // mozilla_IOInterposer_h
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