Ipc::ReadWriteLock Class Reference

#include <ReadWriteLock.h>

Collaboration diagram for Ipc::ReadWriteLock:

Public Member Functions
	ReadWriteLock ()
bool	lockShared ()
	lock for reading or return false
bool	lockExclusive ()
	lock for modification or return false
bool	lockHeaders ()
	lock for [readable] metadata update or return false
void	unlockShared ()
	undo successful sharedLock()
void	unlockExclusive ()
	undo successful exclusiveLock()
void	unlockHeaders ()
	undo successful lockHeaders()
void	switchExclusiveToShared ()
bool	unlockSharedAndSwitchToExclusive ()
void	startAppending ()
	writer keeps its lock but also allows reading
bool	stopAppendingAndRestoreExclusive ()
void	updateStats (ReadWriteLockStats &stats) const
	adds approximate current stats to the supplied ones

Public Attributes
std::atomic< uint32_t >	readers
	number of reading users
std::atomic< bool >	writing
	there is a writing user (there can be at most 1)
std::atomic< bool >	appending
	the writer has promised to only append
std::atomic_flag	updating
	a reader is updating metadata/headers

Private Member Functions
bool	finalizeExclusive ()

Private Attributes
std::atomic< uint32_t >	readLevel
	number of users reading (or trying to)
std::atomic< uint32_t >	writeLevel
	number of users writing (or trying to write)

Detailed Description

an atomic readers-writer or shared-exclusive lock suitable for maps/tables Also supports reading-while-appending mode when readers and writer are allowed to access the same locked object because the writer promises to only append new data and all size-related object properties are atomic.

Definition at line 26 of file ReadWriteLock.h.

Constructor & Destructor Documentation

ReadWriteLock()

Ipc::ReadWriteLock::ReadWriteLock ( )

inline

Definition at line 29 of file ReadWriteLock.h.

Member Function Documentation

finalizeExclusive()

bool Ipc::ReadWriteLock::finalizeExclusive ( )

private

common lockExclusive() and unlockSharedAndSwitchToExclusive() logic: either finish exclusive locking or bail properly

Precondition

The caller must (be the first to) increment writeLevel.

Returns

whether we got the exclusive lock

Definition at line 28 of file ReadWriteLock.cc.

References appending, assert, readLevel, writeLevel, and writing.

lockExclusive()

bool Ipc::ReadWriteLock::lockExclusive

(

)

Definition at line 53 of file ReadWriteLock.cc.

Referenced by Ipc::MemMap::free(), Ipc::StoreMap::freeEntry(), Ipc::StoreMap::freeEntryByKey(), Ipc::MemMap::openForWritingAt(), Ipc::StoreMap::openForWritingAt(), and Ipc::StoreMap::purgeOne().

lockHeaders()

bool Ipc::ReadWriteLock::lockHeaders

(

)

Definition at line 63 of file ReadWriteLock.cc.

Referenced by Ipc::StoreMap::openForUpdating().

lockShared()

bool Ipc::ReadWriteLock::lockShared

(

)

Definition at line 41 of file ReadWriteLock.cc.

Referenced by Ipc::StoreMap::freeEntryByKey(), Ipc::MemMap::openForReadingAt(), and Ipc::StoreMap::openForReadingAt().

startAppending()

void Ipc::ReadWriteLock::startAppending

(

)

Definition at line 124 of file ReadWriteLock.cc.

References assert.

Referenced by Ipc::StoreMap::startAppending().

stopAppendingAndRestoreExclusive()

bool Ipc::ReadWriteLock::stopAppendingAndRestoreExclusive

(

)

writer keeps its lock and disallows future readers

Returns

whether access became exclusive (i.e. no readers) \prec appending is true

Definition at line 131 of file ReadWriteLock.cc.

References assert.

Referenced by Ipc::StoreMap::abortWriting().

switchExclusiveToShared()

void Ipc::ReadWriteLock::switchExclusiveToShared

(

)

stop writing, start reading

Definition at line 100 of file ReadWriteLock.cc.

References assert.

Referenced by Ipc::StoreMap::closeForUpdating(), Ipc::MemMap::switchWritingToReading(), and Ipc::StoreMap::switchWritingToReading().

unlockExclusive()

void Ipc::ReadWriteLock::unlockExclusive

(

)

Definition at line 83 of file ReadWriteLock.cc.

References assert.

Referenced by Ipc::StoreMap::abortWriting(), Ipc::MemMap::closeForWriting(), Ipc::StoreMap::closeForWriting(), Ipc::StoreMap::forgetWritingEntry(), Ipc::StoreMap::freeChain(), Ipc::StoreMap::freeEntryByKey(), Ipc::MemMap::freeLocked(), Ipc::MemMap::openForWritingAt(), Ipc::StoreMap::openForWritingAt(), and Ipc::StoreMap::purgeOne().

unlockHeaders()

void Ipc::ReadWriteLock::unlockHeaders

(

)

Definition at line 92 of file ReadWriteLock.cc.

References Ipc::AssertFlagIsSet().

Referenced by Ipc::StoreMap::abortUpdating(), and Ipc::StoreMap::closeForUpdating().

unlockShared()

void Ipc::ReadWriteLock::unlockShared

(

)

Definition at line 75 of file ReadWriteLock.cc.

References assert.

Referenced by Ipc::MemMap::closeForReading(), Ipc::StoreMap::closeForReading(), Ipc::StoreMap::freeEntryByKey(), Ipc::MemMap::openForReadingAt(), and Ipc::StoreMap::openForReadingAt().

unlockSharedAndSwitchToExclusive()

bool Ipc::ReadWriteLock::unlockSharedAndSwitchToExclusive

(

)

same as unlockShared() but also attempts to get a writer lock beforehand

Returns

whether the writer lock was acquired

Definition at line 109 of file ReadWriteLock.cc.

References assert.

updateStats()

void Ipc::ReadWriteLock::updateStats

(

ReadWriteLockStats &

stats

)

const

Definition at line 148 of file ReadWriteLock.cc.

References Ipc::ReadWriteLockStats::appenders, Ipc::ReadWriteLockStats::count, Ipc::ReadWriteLockStats::idle, Ipc::ReadWriteLockStats::readable, Ipc::ReadWriteLockStats::readers, Ipc::ReadWriteLockStats::writeable, and Ipc::ReadWriteLockStats::writers.

Member Data Documentation

appending

std::atomic<bool> Ipc::ReadWriteLock::appending

Definition at line 56 of file ReadWriteLock.h.

Referenced by Ipc::StoreMap::abortWriting(), finalizeExclusive(), and Ipc::operator<<().

readers

std::atomic<uint32_t> Ipc::ReadWriteLock::readers

mutable

Definition at line 54 of file ReadWriteLock.h.

Referenced by Ipc::operator<<(), Transients::readers(), Ipc::MemMapSlot::reading(), and Ipc::StoreMapAnchor::reading().

readLevel

std::atomic<uint32_t> Ipc::ReadWriteLock::readLevel

mutableprivate

Definition at line 62 of file ReadWriteLock.h.

Referenced by finalizeExclusive().

updating

std::atomic_flag Ipc::ReadWriteLock::updating

Definition at line 57 of file ReadWriteLock.h.

Referenced by Ipc::StoreMap::abortUpdating(), and Ipc::StoreMap::closeForUpdating().

writeLevel

std::atomic<uint32_t> Ipc::ReadWriteLock::writeLevel

private

Definition at line 63 of file ReadWriteLock.h.

Referenced by finalizeExclusive().

writing

std::atomic<bool> Ipc::ReadWriteLock::writing

Definition at line 55 of file ReadWriteLock.h.

Referenced by finalizeExclusive(), Ipc::operator<<(), Ipc::MemMapSlot::writing(), and Ipc::StoreMapAnchor::writing().

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The documentation for this class was generated from the following files:

• squid/src/ipc/ReadWriteLock.h
• squid/src/ipc/ReadWriteLock.cc