shared data (original) (raw)

music

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summary

This subchapter looks at shared data.

stub section

This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.

Professors are invited to give feedback on both the proposed contents and the propsed order of this text book. Send commentary to Milo, PO Box 1361, Tustin, California, 92781, USA.

shared data

This subchapter looks at shared data.

“11 An Ada program is composed of one or more program units. Program units may be subprograms (which define executable algorithms), packages (which define collections of entities), task units (which define concurrent computations), protected units (which define operations for the coordinated sharing of data between tasks), or generic units (which define parameterized forms of packages and subprograms). Each program unit normally consists of two parts: a specification, containing the information that must be visible to other units, and a body, containing the implementation details, which need not be visible to other units. Most program units can be compiled separately.” —:Ada-Europe’s Ada Reference Manual: Introduction: Language Summary See legal information

“18 A task unit is the basic unit for defining a task whose sequence of actions may be executed concurrently with those of other tasks. Such tasks may be implemented on multicomputers, multiprocessors, or with interleaved execution on a single processor. A task unit may define either a single executing task or a task type permitting the creation of any number of similar tasks.” —:Ada-Europe’s Ada Reference Manual: Introduction: Language Summary See legal information

“19/2 A protected unit is the basic unit for defining protected operations for the coordinated use of data shared between tasks. Simple mutual exclusion is provided automatically, and more elaborate sharing protocols can be defined. A protected operation can either be a subprogram or an entry. A protected entry specifies a Boolean expression (an entry barrier) that must be True before the body of the entry is executed. A protected unit may define a single protected object or a protected type permitting the creation of several similar objects.” —:Ada-Europe’s Ada Reference Manual: Introduction: Language Summary See legal information

assembly language instructions

Multiprocessor instructions are used to coordinate activity between multiple processors.

Some multiprocessor instructions are designed to allow the processors to communicate with each other. A test and set instruction is used to implement flags or semaphores between processors. A compare and swap instruction is used to implement more sophsticated communications between multiple processors (such as counters or queue pointers) or secure updates of shared system control data structures in a multi-processing environment. Interlocked instructions are used to update counters, flags, and semaphores while locking out any other processors or devices from changing or reading the memory location while it is being updated.

TAS Test and Set an Operand; Motorola 680x0; tests the current value of the operand at the effective address in memory or a data register (obviously, data register operands aren’t multiprocessor, but the instruction still works) and sets or clears the N (negative) and Z (zero) condition codes accordingly, then sets the high order bit of the operand to one; this operation uses a read-modify-write memory cycle that completes the operation without interruption; sets or clears flags
CAS Compare and Swap with Operand; Motorola 680x0; Compares the operand at an effective address in memory to a compare operand in a data register, if the operands are equal, the update operand is transferred from a data register to the original effective address, if the operands are unequal, the operand at the effective address is transferred to the data register that contained the compare operand; this operation uses a read-modify-write memory cycle that completes the operation without interruption; sets or clears flags
CAS2 Dual Operand Compare and Swap; Motorola 680x0; Compares the operand at an effective address in memory to a compare operand in a data register, if the operands are equal, compares the operand at a second effective address in memory to a second compare operand in a data register, if the second operand is also equal, the update operands are transferred from a data register to the pair of original effective addresses, if either pair of operands are unequal, the operands at the pair of effective addresses are transferred to the data registers that contained the compare operands; this operation uses a read-modify-write memory cycle that completes the operation without interruption; sets or clears flags
ADAWI Add Aligned Word Interlocked; DEC VAX; adds (16 bit integer) a source operand from a register or memory to a memory location that is word aligned while interlocking the memory location so that no other processor or device can read or write to the interlocked memory location, used to maintain operating system resource usage counts; and sets or clears flags
INSQHI Insert Entry into Queue at Head, Interlocked; DEC VAX; inserts a forward and backward linked entry into the head of a queue, checking first that all memory accesses can be performed without memory management exception, uses interlock to allow a queue to be shared by multiple prcoesses even in a multiprocessor environment without any additional synchronization
INSQTI Insert Entry into Queue at Tail, Interlocked; DEC VAX; inserts a forward and backward linked entry into the tail of a queue, checking first that all memory accesses can be performed without memory management exception, uses interlock to allow a queue to be shared by multiple prcoesses even in a multiprocessor environment without any additional synchronization
INSQUE Insert Entry in Queue; DEC VAX; inserts a forward and backward linked entry into the designated location in a queue, checking first that all memory accesses can be performed without memory management exception, non-interruptible so two or more processes on the same processor may share the same queue without conflict including queues shared with interrupt service routines
REMQHI Remove Entry from Queue at Head, Interlocked; DEC VAX; removes a forward and backward linked entry from the head of a queue, checking first that all memory accesses can be performed without memory management exception, uses interlock to allow a queue to be shared by multiple prcoesses even in a multiprocessor environment without any additional synchronization
INSQTI Remove Entry from Queue at Tail, Interlocked; DEC VAX; removes a forward and backward linked entry from the tail of a queue, checking first that all memory accesses can be performed without memory management exception, uses interlock to allow a queue to be shared by multiple prcoesses even in a multiprocessor environment without any additional synchronization
INSQUE Remove Entry from Queue; DEC VAX; removes a forward and backward linked entry from the designated location in a queue, checking first that all memory accesses can be performed without memory management exception, non-interruptible so two or more processes on the same processor may share the same queue without conflict including queues shared with interrupt service routines

free music player coding example

Coding example: I am making heavily documented and explained open source code for a method to play music for free — almost any song, no subscription fees, no download costs, no advertisements, all completely legal. This is done by building a front-end to YouTube (which checks the copyright permissions for you).

View music player in action: www.musicinpublic.com/.

Create your own copy from the original source code/ (presented for learning programming).

Because I no longer have the computer and software to make PDFs, the book is available as an HTML file, which you can convert into a PDF.

†UNIX used as a generic term unless specifically used as a trademark (such as in the phrase “UNIX certified”). UNIX is a registered trademark in the United States and other countries, licensed exclusively through X/Open Company Ltd.