gecko-dev/dom/commandhandler/nsCommandParams.h
Nathan Froyd e7b3b3140d Bug 1415980 - make hash keys movable and not copyable; r=erahm
Everything that goes in a PLDHashtable (and its derivatives, like
nsTHashtable) needs to inherit from PLDHashEntryHdr. But through a lack
of enforcement, copy constructors for these derived classes didn't
explicitly invoke the copy constructor for PLDHashEntryHdr (and the
compiler didn't invoke the copy constructor for us). Instead,
PLDHashTable explicitly copied around the bits that the copy constructor
would have.

The current setup has two problems:

1) Derived classes should be using move construction, not copy
   construction, since anything that's shuffling hash table keys/entries
   around will be using move construction.

2) Derived classes should take responsibility for transferring bits of
   superclass state around, and not rely on something else to handle that.

The second point is not a huge problem for PLDHashTable (PLDHashTable
only has to copy PLDHashEntryHdr's bits in a single place), but future
hash table implementations that might move entries around more
aggressively would have to insert compensation code all over the
place. Additionally, if moving entries is implemented via memcpy (which
is quite common), PLDHashTable copying around bits *again* is
inefficient.

Let's fix all these problems in one go, by:

1) Explicitly declaring the set of constructors that PLDHashEntryHdr
   implements (and does not implement). In particular, the copy
   constructor is deleted, so any derived classes that attempt to make
   themselves copyable will be detected at compile time: the compiler
   will complain that the superclass type is not copyable.

This change on its own will result in many compiler errors, so...

2) Change any derived classes to implement move constructors instead of
   copy constructors. Note that some of these move constructors are,
   strictly speaking, unnecessary, since the relevant classes are moved
   via memcpy in nsTHashtable and its derivatives.
2018-09-20 11:20:36 -04:00

184 lines
4.9 KiB
C++

/* -*- 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 nsCommandParams_h
#define nsCommandParams_h
#include "mozilla/ErrorResult.h"
#include "nsString.h"
#include "nsICommandParams.h"
#include "nsCOMPtr.h"
#include "PLDHashTable.h"
class nsCommandParams : public nsICommandParams
{
typedef mozilla::ErrorResult ErrorResult;
typedef mozilla::IgnoredErrorResult IgnoredErrorResult;
public:
nsCommandParams();
NS_DECL_ISUPPORTS
NS_DECL_NSICOMMANDPARAMS
bool GetBool(const char* aName, ErrorResult& aRv) const;
inline bool GetBool(const char* aName) const
{
IgnoredErrorResult error;
return GetBool(aName, error);
}
int32_t GetInt(const char* aName, ErrorResult& aRv) const;
inline int32_t GetInt(const char* aName) const
{
IgnoredErrorResult error;
return GetInt(aName, error);
}
double GetDouble(const char* aName, ErrorResult& aRv) const;
inline double GetDouble(const char* aName) const
{
IgnoredErrorResult error;
return GetDouble(aName, error);
}
nsresult GetString(const char* aName, nsAString& aValue) const;
nsresult GetCString(const char* aName, nsACString& aValue) const;
already_AddRefed<nsISupports>
GetISupports(const char* aName, ErrorResult& aRv) const;
inline already_AddRefed<nsISupports> GetISupports(const char* aName) const
{
IgnoredErrorResult error;
return GetISupports(aName, error);
}
nsresult SetBool(const char* aName, bool aValue);
nsresult SetInt(const char* aName, int32_t aValue);
nsresult SetDouble(const char* aName, double aValue);
nsresult SetString(const char* aName, const nsAString& aValue);
nsresult SetCString(const char* aName, const nsACString& aValue);
nsresult SetISupports(const char* aName, nsISupports* aValue);
protected:
virtual ~nsCommandParams();
struct HashEntry : public PLDHashEntryHdr
{
nsCString mEntryName;
uint8_t mEntryType;
union
{
bool mBoolean;
int32_t mLong;
double mDouble;
nsString* mString;
nsCString* mCString;
} mData;
nsCOMPtr<nsISupports> mISupports;
HashEntry(uint8_t aType, const char* aEntryName)
: mEntryName(aEntryName)
, mEntryType(aType)
, mData()
{
Reset(mEntryType);
}
explicit HashEntry(const HashEntry& aRHS)
: mEntryType(aRHS.mEntryType)
{
Reset(mEntryType);
switch (mEntryType) {
case eBooleanType:
mData.mBoolean = aRHS.mData.mBoolean;
break;
case eLongType:
mData.mLong = aRHS.mData.mLong;
break;
case eDoubleType:
mData.mDouble = aRHS.mData.mDouble;
break;
case eWStringType:
NS_ASSERTION(aRHS.mData.mString, "Source entry has no string");
mData.mString = new nsString(*aRHS.mData.mString);
break;
case eStringType:
NS_ASSERTION(aRHS.mData.mCString, "Source entry has no string");
mData.mCString = new nsCString(*aRHS.mData.mCString);
break;
case eISupportsType:
mISupports = aRHS.mISupports.get();
break;
default:
NS_ERROR("Unknown type");
}
}
~HashEntry() { Reset(eNoType); }
void Reset(uint8_t aNewType)
{
switch (mEntryType) {
case eNoType:
break;
case eBooleanType:
mData.mBoolean = false;
break;
case eLongType:
mData.mLong = 0;
break;
case eDoubleType:
mData.mDouble = 0.0;
break;
case eWStringType:
delete mData.mString;
mData.mString = nullptr;
break;
case eISupportsType:
mISupports = nullptr;
break;
case eStringType:
delete mData.mCString;
mData.mCString = nullptr;
break;
default:
NS_ERROR("Unknown type");
}
mEntryType = aNewType;
}
};
HashEntry* GetNamedEntry(const char* aName) const;
HashEntry* GetOrMakeEntry(const char* aName, uint8_t aEntryType);
protected:
static PLDHashNumber HashKey(const void* aKey);
static bool HashMatchEntry(const PLDHashEntryHdr* aEntry, const void* aKey);
static void HashMoveEntry(PLDHashTable* aTable, const PLDHashEntryHdr* aFrom,
PLDHashEntryHdr* aTo);
static void HashClearEntry(PLDHashTable* aTable, PLDHashEntryHdr* aEntry);
PLDHashTable mValuesHash;
static const PLDHashTableOps sHashOps;
};
nsCommandParams*
nsICommandParams::AsCommandParams()
{
return static_cast<nsCommandParams*>(this);
}
const nsCommandParams*
nsICommandParams::AsCommandParams() const
{
return static_cast<const nsCommandParams*>(this);
}
#endif // nsCommandParams_h