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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
#ifndef mozilla_IOInterposer_h
#define mozilla_IOInterposer_h
#include "mozilla/Attributes.h"
#include "mozilla/TimeStamp.h"
#include "nsString.h"
namespace mozilla {
/**
* Interface for I/O interposer observers. This is separate from the
* IOInterposer because we have multiple uses for these observations.
*/
class IOInterposeObserver {
public:
enum Operation {
OpNone = 0,
OpCreateOrOpen = (1 << 0),
OpRead = (1 << 1),
OpWrite = (1 << 2),
OpFSync = (1 << 3),
OpStat = (1 << 4),
OpClose = (1 << 5),
OpNextStage =
(1 << 6), // Meta - used when leaving startup, entering shutdown
OpWriteFSync = (OpWrite | OpFSync),
OpAll = (OpCreateOrOpen | OpRead | OpWrite | OpFSync | OpStat | OpClose),
OpAllWithStaging = (OpAll | OpNextStage)
};
/** A representation of an I/O observation */
class Observation {
protected:
/**
* This constructor is for use by subclasses that are intended to take
* timing measurements via RAII. The |aShouldReport| parameter may be
* used to make the measurement and reporting conditional on the
* satisfaction of an arbitrary predicate that was evaluated
* in the subclass. Note that IOInterposer::IsObservedOperation() is
* always ANDed with aShouldReport, so the subclass does not need to
* include a call to that function explicitly.
*/
Observation(Operation aOperation, const char* aReference,
bool aShouldReport = true);
public:
/**
* Since this constructor accepts start and end times, it does *not* take
* its own timings, nor does it report itself.
*/
Observation(Operation aOperation, const TimeStamp& aStart,
const TimeStamp& aEnd, const char* aReference);
/**
* Operation observed, this is one of the individual Operation values.
* Combinations of these flags are only used when registering observers.
*/
Operation ObservedOperation() const { return mOperation; }
/**
* Return the observed operation as a human-readable string.
*/
const char* ObservedOperationString() const;
/** Time at which the I/O operation was started */
TimeStamp Start() const { return mStart; }
/**
* Time at which the I/O operation ended, for asynchronous methods this is
* the time at which the call initiating the asynchronous request returned.
*/
TimeStamp End() const { return mEnd; }
/**
* Duration of the operation, for asynchronous I/O methods this is the
* duration of the call initiating the asynchronous request.
*/
TimeDuration Duration() const { return mEnd - mStart; }
/**
* IO reference, function name or name of component (sqlite) that did IO
* this is in addition the generic operation. This attribute may be platform
* specific, but should only take a finite number of distinct values.
* E.g. sqlite-commit, CreateFile, NtReadFile, fread, fsync, mmap, etc.
* I.e. typically the platform specific function that did the IO.
*/
const char* Reference() const { return mReference; }
virtual const char* FileType() const { return "File"; }
/** Request filename associated with the I/O operation, empty if unknown */
virtual void Filename(nsAString& aString) { aString.Truncate(); }
virtual ~Observation() = default;
protected:
void Report();
Operation mOperation;
TimeStamp mStart;
TimeStamp mEnd;
const char* mReference; // Identifies the source of the Observation
bool mShouldReport; // Measure and report if true
};
/**
* Invoked whenever an implementation of the IOInterposeObserver should
* observe aObservation. Implement this and do your thing...
* But do consider if it is wise to use IO functions in this method, they are
* likely to cause recursion :)
* At least, see PoisonIOInterposer.h and register your handle as a debug file
* even, if you don't initialize the poison IO interposer, someone else might.
*
* Remark: Observations may occur on any thread.
*/
virtual void Observe(Observation& aObservation) = 0;
virtual ~IOInterposeObserver() = default;
protected:
/**
* We don't use NS_IsMainThread() because we need to be able to determine the
* main thread outside of XPCOM Initialization. IOInterposer observers should
* call this function instead.
*/
static bool IsMainThread();
};
/**
* These functions are responsible for ensuring that events are routed to the
* appropriate observers.
*/
namespace IOInterposer {
/**
* This function must be called from the main-thread when no other threads are
* running before any of the other methods on this class may be used.
*
* IO reports can however, safely assume that IsObservedOperation() will
* return false until the IOInterposer is initialized.
*
* Remark, it's safe to call this method multiple times, so just call it when
* you to utilize IO interposing.
*
* Using the IOInterposerInit class is preferred to calling this directly.
*/
bool Init();
/**
* This function must be called from the main thread, and furthermore
* it must be called when no other threads are executing. Effectively
* restricting us to calling it only during shutdown.
*
* Callers should take care that no other consumers are subscribed to events,
* as these events will stop when this function is called.
*
* In practice, we don't use this method as the IOInterposer is used for
* late-write checks.
*/
void Clear();
/**
* This function immediately disables IOInterposer functionality in a fast,
* thread-safe manner. Primarily for use by the crash reporter.
*/
void Disable();
/**
* This function re-enables IOInterposer functionality in a fast, thread-safe
* manner. Primarily for use by the crash reporter.
*/
void Enable();
/**
* Report IO to registered observers.
* Notice that the reported operation must be either OpRead, OpWrite or
* OpFSync. You are not allowed to report an observation with OpWriteFSync or
* OpAll, these are just auxiliary values for use with Register().
*
* If the IO call you're reporting does multiple things, write and fsync, you
* can choose to call Report() twice once with write and once with FSync. You
* may not call Report() with OpWriteFSync! The Observation::mOperation
* attribute is meant to be generic, not perfect.
*
* Notice that there is no reason to report an observation with an operation
* which is not being observed. Use IsObservedOperation() to check if the
* operation you are about to report is being observed. This is especially
* important if you are constructing expensive observations containing
* filename and full-path.
*
* Remark: Init() must be called before any IO is reported. But
* IsObservedOperation() will return false until Init() is called.
*/
void Report(IOInterposeObserver::Observation& aObservation);
/**
* Return whether or not an operation is observed. Reporters should not
* report operations that are not being observed by anybody. This mechanism
* allows us to avoid reporting I/O when no observers are registered.
*/
bool IsObservedOperation(IOInterposeObserver::Operation aOp);
/**
* Register IOInterposeObserver, the observer object will receive all
* observations for the given operation aOp.
*
* Remarks:
* - Init() must be called before observers are registered.
* - The IOInterposeObserver object should be static, because it could still be
* used on another thread shortly after Unregister().
*/
void Register(IOInterposeObserver::Operation aOp,
IOInterposeObserver* aStaticObserver);
/**
* Unregister an IOInterposeObserver for a given operation
* Remark: It is always safe to unregister for all operations, even if yoú
* didn't register for them all.
* I.e. IOInterposer::Unregister(IOInterposeObserver::OpAll, aObserver)
*
* Remarks:
* - Init() must be called before observers are registered.
* - The IOInterposeObserver object should be static, because it could still be
* used on another thread shortly after this Unregister() call.
*/
void Unregister(IOInterposeObserver::Operation aOp,
IOInterposeObserver* aStaticObserver);
/**
* Registers the current thread with the IOInterposer. This must be done to
* ensure that per-thread data is created in an orderly fashion.
* We could have written this to initialize that data lazily, however this
* could have unintended consequences if a thread that is not aware of
* IOInterposer was implicitly registered: its per-thread data would never
* be deleted because it would not know to unregister itself.
*
* @param aIsMainThread true if IOInterposer should treat the current thread
* as the main thread.
*/
void RegisterCurrentThread(bool aIsMainThread = false);
/**
* Unregisters the current thread with the IOInterposer. This is important
* to call when a thread is shutting down because it cleans up data that
* is stored in a TLS slot.
*/
void UnregisterCurrentThread();
/**
* Called to inform observers that the process has transitioned out of the
* startup stage or into the shutdown stage. Main thread only.
*/
void EnteringNextStage();
} // namespace IOInterposer
class MOZ_RAII AutoIOInterposer {
public:
AutoIOInterposer() = default;
void Init() {
#if defined(EARLY_BETA_OR_EARLIER)
IOInterposer::Init();
#endif
}
~AutoIOInterposer() {
#if defined(EARLY_BETA_OR_EARLIER)
IOInterposer::Clear();
#endif
}
};
class MOZ_RAII AutoIOInterposerDisable final {
public:
explicit AutoIOInterposerDisable() { IOInterposer::Disable(); }
~AutoIOInterposerDisable() { IOInterposer::Enable(); }
private:
};
} // namespace mozilla
#endif // mozilla_IOInterposer_h