Authors
- Richard Frith-Macdonald (
rfm@gnu.org)
-
Copyright: (C) 2011 Free Software Foundation, Inc.
- Declared in:
- GSFIFO.h
GSFIFO manages a first-in-first-out queue of items.
Items in the queue are
NOT retained
objects... memory management is not the job of this
class and it is not intended to be treated as a
'collection', rather its role is intended to be
that of an inter-thread coordination mechanism.
Instances of the GSFIFO class are intended to
support the producer-consumer model of processing.
The ideal example is that of a production line, where you
have a stream of items to be processed and while that
processing can be broken down into separate
stages, they must be done in a particular order. The
FIFO is used as the link betwen those stages, ensuring
that the required ordering is maintained even when
separate threads handle each stage.
Where
there is a single producer and a single consumer
thread, a fast lock-free algorthm is used to get/pu
items from the FIFO.
To minimise the overheads
of using the FIFO, we provide inline functions to support
the addition of items in the single producer thread case
and to support the removal of items in the single
consumer thread case. When operating that way, the
overhead of using the FIFO is only a few CPU cycles
and it becomes reasonable to split sequentional
processing into a
long series of
small operations each handled by a separate thread
(making effective use of a multi-cpu machine).
The FIFO may also be useful where you don't have a
strictly sequential process to manage, but some
parts need to be sequential... in these cases it may
make sense to have multiple consumers and/or producers.
In these cases, some locking is required and the use of
the inline functions is not allowed (you must call the
-get
and
-put:
methods.
It is recommended that you create FIFOs using
the
-initWithName:
method so that you can easily use the NSUserDefaults
system to adjust their configurations to tests/tweak
performance.
Instance Variables
Method summary
+ (NSString*)
stats;
Return statistics for all current GSFIFO instances.
Statistics for FIFOs which are configued to
be lock-free are empty (listing the name only) except
where we can safely obtain get or put stats because
the FIFOs consumer/producer thread is the same as the
current thread.
- (
NSUInteger)
count;
Returns the approximate number of items in the
FIFO.
- (void*)
get;
Gets the next item from the FIFO, blocking if
necessary until an item is available. Raises an
exception if the FIFO is configured with a
timeout and it is exceeded.
Implemented
using
-get:count:shouldBlock:
- (unsigned)
get: (void**)buf
count: (unsigned)count
shouldBlock: (BOOL)block;
Reads up to count items from the FIFO into
buf. If block is
YES, this blocks if necessary until at
least one item is available, and raises an exception
if the FIFO is configured with a timeout and it is
exceeded.
Returns the number of items
actually read.
- (id)
initWithCapacity: (uint32_t)c
granularity: (uint16_t)g
timeout: (uint16_t)t
multiProducer: (BOOL)mp
multiConsumer: (BOOL)mc
boundaries: (NSArray*)a
name: (NSString*)n;
This is a designated initialiser for the class.
Initialises the receiver with the specified
capacity (buffer size).
The capacity must
lie in the range from one to
a million,
othewrwise the receiver is deallocated and this
method returns
nil.
If the
granularity value is non-zero, it is treated as
the maximum time in milliseconds for which
a
-get
or
-put:
operation
will pause between successive attempts.
If the
timeout value is non-zero, it is treated as the
total time in milliseconds for which
a
-get
or
-put:
operation
may block, and
a longer delay will cause
those methods to raise an exception.
If the
multiProducer or multiConsumer flag is
YES, the FIFO is configured to support
multiple producer/consumer threads using locking.
The boundaries array is an ordered list of
NSNumber objects containing time intervals found
boundaries of bands into which to categorise
wait time stats. Any wait whose duration is less than
the interval specified in the Nth element is counted in
the stat's for the Nth band. If this is
nil,
a default set of
bundaries is used. If it is an empty array then
no time based stats are recorded.
The name string
is
a unique identifier for the receiver and
is used when printing diagnostics and statistics. If an
instance with the same name already exists, the
receiveris deallocated and an exception is
raised.
- (id)
initWithCapacity: (uint32_t)c
name: (NSString*)n;
Initialises the receiver as a multi-producer,
multi-consumer FIFO with no timeout and with
default stats gathering enabled.
However,
these values (including the supplied capacity) may be
overridden as specified in
-initWithName:
- (id)
initWithName: (NSString*)n;
Initialises the receiver using the specified
name and obtaining other details from the
NSUserDefaults system using defaults keys
where 'NNN' is the supplied name.
The
GSFIFOCapacityNNN default specifies the
capacity for the FIFO, and if missing a capacity
of 1000 is assumed.
The GSFIFOGranularityNNN
integer is zero by default.
The
GSFIFOTimeoutNNN integer is zero by
default.
The GSFIFOSingleConsumerNNN
boolean is NO by default.
The
GSFIFOSingleProducerNNN boolean is
NO by default.
The
GSFIFOBoundariesNNN array is missing by
default.
- (void)
put: (void*)item;
Adds an
item to the FIFO, blocking if
necessary until there is space in the buffer.
Raises an exception if the FIFO is configured with a
timeout and it is exceeded.br /> Implemented using
-put:count:shouldBlock:
- (unsigned)
put: (void**)buf
count: (unsigned)count
shouldBlock: (BOOL)block;
Writes up to count items from
buf into the FIFO. If block is
YES, this blocks if necessary until at
least one item can be written, and raises an
exception if the FIFO is configured with a
timeout and it is exceeded.
Returns the
number of items actually written.
- (NSString*)
stats;
Return any available statistics for the receiver.
- (NSString*)
statsGet;
Return statistics on get operations for the
receiver.
NB. If the recever is not
configured for multiple consumers, this method
may only be called from the single consumer thread.
- (NSString*)
statsPut;
Return statistics on put operations for the
receiver.
NB. If the recever is not
configured for multiple producers, this method
may only be called from the single producer thread.
- (void*)
tryGet;
Checks the FIFO and returns the first available item
or NULL if the FIFO is empty.
Implemented using
-get:count:shouldBlock:
- (BOOL)
tryPut: (void*)item;
Attempts to put an
item into the FIFO,
returning
YES on success or
NO if the FIFO is full.
Implemented using
-put:count:shouldBlock:
Instance Variables for GSFIFO Class
@public uint32_t _capacity;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
@public uint64_t _getTryFailure;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
@public uint64_t _getTrySuccess;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
@public volatile uint64_t _head;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
@public void** _items;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
@public uint64_t _putTryFailure;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
@public uint64_t _putTrySuccess;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
@public volatile uint64_t _tail;
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
void* GSGetFastFIFO(GSFIFO* receiver);
Function to efficiently get an item from a fast
FIFO, blocking if necessary until an item is available
or the timeout occurs.
Warning... only for use if
the FIFO is NOT configured for multiple consumers.
void* GSGetFastNonBlockingFIFO(GSFIFO* receiver);
Function to efficiently get an item from a fast
FIFO.
Returns NULL if the FIFO is empty.
Warning... only for use if the FIFO is NOT configured
for multiple consumers.
void GSPutFastFIFO(GSFIFO* receiver, void* item);
Function to efficiently put an item to a
fast FIFO, blocking if necessary until there is space in
the FIFO or until the timeout occurs.
Warning...
only for use if the FIFO is NOT configured for multiple
producers.
BOOL GSPutFastNonBlockingFIFO(GSFIFO* receiver, void* item);
Function to efficiently put an item to a
fast FIFO.
Returns YES on success,
NO on failure (FIFO is full).
Warning... only for use if the FIFO is NOT configured
for multiple producers.