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Dequesterity is a set of Ada 2005 generics that provide various forms of general purpose buffer containers. Buffers may be used as deques, queues, ring buffers, stacks, double ended stacks, vectors, priority queues, and similar abstractions. The generics are combinable and pluggable such that lower level buffer implementations may be combined with higher level buffer generics to create a wide selection of buffer types with specific sets of functionality. Lower level buffer implementations include bounded and unbounded buffer forms. Higher level buffer implementations add can concurrency support, priority queuing, and streaming of heterogeneous objects. Buffer instances may be streamed, or may be accessed remotely using the Distributed Systems Annex. Most buffers can store their state persistently. Some buffer implementations operate entirely on secondary (file based) storage. The buffers may be instantiated with user defined types, and indefinite buffer forms also exist. The interface to the buffers is modelled after the Ada 2005 container libraries. Dequesterity is free software. See the file COPYING for copying permission. Most of the source code is released under the GMGPL (GNAT Modified GPL) See the individual source files for details. Any comments on the generics would be greatly appreciated. Please send comments to brad.moore@shaw.ca 0.0 DOWNLOADING ============== The latest stable release and older releases may be downloaded from; https://sourceforge.net/projects/dequesterity/files/ For those who want the current development versions of the source they can download using git (http://git-scm.com/) by issuing the following commands mkdir sandbox cd sandbox git clone git://git.code.sf.net/p/dequesterity/code dequesterity-src The current development version typically will correspond to the latest stable release, but may at times be unstable when new features are being worked on. 1.0 INTRODUCTION ================ What is a buffer? ----------------- A Buffer is a general purpose container that is implemented as a circular array of elements, where the element type can be specified by the client. Many forms of buffer generics are provided, allowing one to select an implementation with a very specific set of features. Each buffer exists as a separate generic library unit. The buffer implementations are designed to be swappable and combinable, so that various feature sets may be provided simply by combining lower level implementations that have desired features. What buffers exist? ------------------- There currently exist 70 generic buffers types, 10 stream buffer types, and 25 preinstantiated string buffer types. The generic buffers may be instantiated with user defined types. The priority buffers maintain a list of objects that are sorted by a user defined sorting criteria. The stream buffers allow storing heterogeneous objects into a buffer. Any streamable object may be stored and retrieved into a stream buffer. The string buffers are instantiations of the generic buffers for the Ada Character and String types. It is thought that character based buffers would be somewhat common, and the string buffers also provide a good example on how to instantiate and use the generic buffers. All buffers intended for client usage may be found under the "Classes" subfolder under the "Buffers" folder. The buffers folder provides the parent package for all the instantiations, depending on whether indefinite buffers are needed or not. All buffers involving constrained element types are child packages of Buffers.ads. All buffers involving unconstrained element types, (i.e. indefinite buffers) are child packages of Indefinite_Buffers.ads. The buffer generic filenames are named using the following convention. buffers-{high_level_implementation}_{low_level_implementation}.ads eg., A buffer generic involving Ravenscar concurrency support using the low level bounded buffer implementation can be found in the following generic. Buffers/Classes/buffers-ravenscar_bounded.ads Some of the buffer generics only utilize low level implementations without specifying a high level implementation. These buffer types are called simple buffers, and thus the name "simple" is specifed in the position for the high_level_implementation name. For example, a simple unbounded buffer can be found under the filename; Buffers/Classes/buffers-simple_unbounded.ads 2.0 Buffer Classification ========================= The low-level (simple) implementations include the following types; 1) Bounded Buffer A buffer that is statically bounded in size, implemented as a circular array 2) Unbounded Buffer An unbounded buffer is a buffer that has a maximum capacity, but whose storage is internally allocated from the heap. An unbounded buffer can grow in size, or shrink as necessary to accomodate the data being stored. An unbounded buffer is internally implemented as an access to Bounded Buffer 3) Segmented Buffer A segmented buffer expands on the idea of an unbounded buffer. An unbounded buffer is a single allocation of a buffer, whereas a segmented buffer consists of numerous segments, where each segment is itself an unbounded buffer. Such a buffer can be useful for example for processing large images in memory. It may not be possible to allocate a single unbounded buffer to hold a large array of data, but it may be possible to perform many smaller allocations to store the same data in memory. Like an unbounded buffer, the storage of a segmented buffer can grow or shrink to accomodate the current amount of data stored in the buffer. 4) Persistent Buffer A persistent buffer is a buffer that is not stored in memory. Rather, it is stored entirely on disk, and manipulated on secondary storage. 5) Scattered Buffer This is more of an experimental buffer type that allows an assortment of other buffers of other types to be treated as a single buffer. This is more of a special purpose buffer, that may not be of interest to general client usage. An intermediate level of buffer abstractions include the priority buffers. A priority buffer maintains a sorted order for the objects in the buffer. Low level buffers may be combined with priority buffers to produce the desired behaviour. Priority buffers may also be used to instantiate the higher level concurrent buffer forms. The higher level concurrency generics provide the following abstractions. 1) Active This concurrency generic implements a buffer as a task. This generic is more of an academic example that demonstrates how task interfaces can be utilized to provide concurrency. It is not generally recommended that clients consider this generic for use, since other generics provide similar functionality, without requiring tasks. 2) Non-Blocking This generic provides concurrency, but has no blocking calls. A call to read from a buffer that has no data will return reporting that no data has been read. Similarly, an attempt to write data into a full buffer will immediately return indicating that the call failed. This concurrency type may be useful for creating Shared_Passive partitions. A Non-Blocking buffer is Ravenscar compliant, since there are no entries associated with the buffer. 3) Passive A passive buffer provides concurrency with blocking calls on reads on an empty buffer, and writes to a full buffer. A passive buffer allows for multiple producers and consumers, and provides two different modes of operation. a) mode 1: Deadlock Detection Capable b) mode 2: Allow Oversized requests If the buffer object is declared with deadlock detection capability, it means any conditional entry calls or timed entry calls can be cancelled without modifying the state of the buffer. Deadlock can be detected through the use of timed entry calls. Deadlock will not occur through calls to the buffer, but if for some reason the buffer if full, and consumer task are not dequeing data from the buffer, then producer tasks can break out of a blocking write, and resume activity. Similarly, if producer tasks are not enqueueing data into the buffer, consumer threads blocked on read requests for an empty buffer can break out of the request and resume activity. The oversized write mode does not support timed entry calls, but in exchange, supports reading and writing vectors of elements of any size into the buffer. The size of the vector may in fact be larger than the capacity of the buffer. Producers and consumers and handled transparently using logic in a protected type, without requiring any additional tasks to coordinate the oversized reads and writes. 4) Passive_lite A passive-lite buffer is a stripped down, less sophisticated version of a passive buffer that only supports deadlock detection. 5) Ravenscar A Ravenscar buffer is a buffer that supports a single reader and a single writer, with blocking calls for writes when the buffer is full, and blocking calls for read requests when the buffer is empty. 3.0 BUFFER LIST =============== a) Simple (Low Level) Buffers simple_bounded simple_unbounded simple_persistent simple_segmented simple_scattered indefinite_simple_bounded indefinite_simple_unbounded indefinite_simple_scattered b) Second Order Buffers - Priority Buffers bounded_priority unbounded_priority persistent_priority segmented_priority - Concurrent Buffers non_blocking_bounded non_blocking_persistent non_blocking_segmented non_blocking_unbounded passive_bounded passive_bounded_lite passive_persistent passive_persistent_lite passive_segmented passive_segmented_lite passive_unbounded passive_unbounded_lite pure_non_blocking_bounded ravenscar_bounded ravenscar_persistent ravenscar_segmented ravenscar_unbounded active_bounded active_persistent active_scattered active_segmented active_unbounded passive_scattered passive_scattered_lite ravenscar_scattered indefinite_non_blocking_bounded indefinite_non_blocking_unbounded indefinite_passive_bounded indefinite_passive_unbounded indefinite_ravenscar_bounded indefinite_ravenscar_unbounded indefinite_simple_bounded indefinite_simple_unbounded indefinite-passive_scattered - Stream Buffers stream_simple_bounded stream_simple_persistent stream_simple_scattered stream_simple_segmented stream_simple_unbounded c) Third Order Buffers - Concurrent Priority Buffers non_blocking_bounded_priority non_blocking_persistent_priority non_blocking_segmented_priority non_blocking_unbounded_priority passive_bounded_priority passive_lite_bounded_priority passive_lite_persistent_priority passive_lite_segmented_priority passive_lite_unbounded_priority passive_persistent_priority passive_segmented_priority passive_unbounded_priority persistent_priority pure_bounded_priority pure_non_blocking_bounded_priority ravenscar_bounded_priority ravenscar_persistent_priority ravenscar_segmented_priority ravenscar_unbounded_priority indefinite_non_blocking_bounded_priority indefinite_non_blocking_unbounded_priority indefinite_passive_bounded_priority indefinite_passive_unbounded_priority indefinite_ravenscar_bounded_priority indefinite_ravenscar_unbounded_priority - Concurrent Stream Buffers stream_ravenscar_bounded.ads stream_ravenscar_persistent.ads stream_ravenscar_scattered.ads stream_ravenscar_segmented.ads stream_buffers_unbounded.ads c) Preinstantiated Character Buffers string_lite_passive_bounded_buffer.ads string_lite_passive_persistent_buffer.ads string_lite_passive_segmented_buffer.ads string_lite_passive_unbounded_buffer.ads string_non_blocking_bounded_buffer.ads string_non_blocking_persistent_buffer.ads string_non_blocking_segmented_buffer.ads string_non_blocking_unbounded_buffer.ads string_passive_bounded_buffer.ads string_passive_persistent_buffer.ads string_passive_segmented_buffer.ads string_passive_unbounded_buffer.ads string_pure_non_blocking_bounded_buffer.ads string_ravenscar_bounded_buffer.ads string_ravenscar_persistent_buffer.ads string_ravenscar_segmented_buffer.ads string_ravenscar_unbounded_buffer.ads string_simple_bounded_buffer.ads string_simple_persistent_buffer.ads string_simple_segmented_buffer.ads string_simple_unbounded_buffer.ads string_active_bounded_buffer.ads string_active_persistent_buffer.ads string_active_segmented_buffer.ads string_active_unbounded_buffer.ads 4.0 BUILD INSTRUCTIONS ====================== - For the Irvine ICC Ada 2005 compiler on Windows, execute the following script to create the Ada 2005 versions of the executables; icm new icm scan -subdir "*.ad?" icm make buffer_demo icm make ravenscar_test icm make test_priority_buffers icm make test_indefinite_priority_buffers You can add other compile flags as well, such as -compile_flags=\"-predef=(f32,lf64) -opt -debug -nochecks\" to turn on optimization, debug, and disable checks. To compile for Irvine ICC on Linux, the script is the same, except that if compile options are used then the options should be enclosed with single quotes, and \" should be replaced with '"'. i.e. -compile_flags='"-predef=(f32,lf64) -opt -debug -nochecks"' - For GNAT Pro, GNAT GPL or GNAT AUX, load the appropriate .gpr file and build the executable from within the ide, or alternatively use gnatmake to perform the equivalent actions described in the .gpr file. 5.0 SUPPORTED TARGETS AND COMPILERS =================================== The generics have been compiled and run on Windows and Linux, using the GNAT 2011 GPL release, and the Irvine ICC Ada 2005 compiler on Windows though in theory any Ada 2005 compiler should be able to compile the code since there are no dependencies on the GNAT run-time. 6.0 TEST EXECUTABLES ==================== Buffer_Demo instantiates a selection of the buffer generics and illustrates some possible usages. Test_Buffers is a more comprehensive test, but can take quite some time to compile due to all the various combinations of generic instantiations. Ravenscar_Test is a simple test program that illustrates a producer/consumer application using one the ravenscar buffer generics. test_priority_buffers allows a simple insertion test into a priority buffer for a variety of the priority buffer generics. test_indefinite_priority_buffers similarly allows insertions of an indefinite string type into a sorted priority buffer, for a variety of the indefinite buffer generics. 7.0 LIMITATIONS =============== NOTE: There is currently a compiler bug in GNAT (GPL 2012) that does not allow the definite priority_buffers (and the test_priority_buffers project) to compile. This does compile using the Irvine ICC compiler, however. On the other hand, the test_indefinite_priority_buffers project does compile under GNAT. So until the GNAT bug is fixed, which hopefully will be in the Ada2013 GPL version of GNAT, the indefinite priority buffers should be used instead of the definite priority buffer generics, or alternatively, use the ICCAda compiler. Note also that any definite type can be used to instantiate an indefinite priority buffer, though the definite versions would ordinarly be preferable, since they do not involve the use of access types. Brad Moore
Source: README, updated 2013-06-23