CSE 12 Week Eight, Lecture Two

Transcription

1 CSE 12 Week Eight, Lecture Two Hw9: Persistence: What: Data existing longer than. Where: In a datafile on. Why: Most programs persist data. - Data going away when program ends is not common. - Users doesn t want to re-enter data every time they start their program. - Limitation to store objects is based on disk availability, not memory availability. - Data objects are only in memory as they are needed. o Memory usage at run time is reduced.

2 The data on disk: How to view the datafiles? Tool: od : Octal Dump, a UNIX utility. Option: -x: display in hexadecimal -c: display is ASCII characters Not all the data in the datafile will be ASCII: - - -

3 Structure of the datafile: - object ( ) followed by many objects. - Allocation starts with. - Space is reserved in the file for root and occupancy from the. o Values of root and occupancy when reserving space are. - values of root and occupancy will be written by. Algorithm: With each insertion of a new TNode: - Append one TNode to the of the datafile. - Each TNode is serialized to disk as one contiguous section of memory in one operation: o Serialization: Writing an object in memory to disk. o TNodes are serialized from to by TNode s. - Each TNode is read from disk as one contiguous section in one operation. o TNodes are read from into by TNode s. - Mechanism of being able to read or write all data fields as one unit of memory: o TNode data is.

4 Differences and similarities from hw8: - One Tree in memory at all times (same as hw8). - Each TNode in the Tree will really be. o If you want to go get a TNode: Read the TNode from disk into memory. o All TNodes in memory are They can once function using that TNode ends. All TNodes will be allocated: o o No more calls to: new delete o Each object that is newly inserted into the Tree consists of updating two TNodes on disk: Ex: left = new TNode (.);// hw8 syntax left is a field of. o For hw9: Need to update! Why: To make that parent - child relationship : o Updated parent goes. - root, left, right are no longer pointers in hw9. o They are now from where. - this_position: o Equivalent to the pointer of memory. o What: The into where when. o Why: Used to be able to.

5 Working with the disk file: - In the fstream class are two private variables that act like disk heads used to read and write data from and to disk: 1. read data ( g or get pointer) 2. write data ( p or put pointer) - Use accessor methods to set and get private variables: - Continuously throughout low level Tree and TNode code: - seek a pointer: o Moves the disk head to a position in the datafile directly before performing a read or a write. - tell where a pointer currently is: o Result is assigned to left, right, root, or this_position - The g and p are like disk heads that automatically advance when you read or write data to the disk file. Observations: Deleted TNodes will remain as unused fragments without. - Data is there, but not. - Similar to many clients that maintain messages locally on your system. - Not good in high security applications. One more aspect to hw9: - ASCII file input. - Supports repeatability in testing. o Go though in more detail next time.

6 The development guide handout. Uses: As a constant companion throughout development of your solution. Not: Just a final validation. ieng6.ucsd.edu% od -x Driver.datafile ^^^^^^^ ^^^^^^^^^ offset root occupancy ^^^^^^^^^ Perform test of the initial ^D without any TNode input a second time and reverify: - Really exercising two different paths through the Tree constructor: 1. File is present, but empty. 2. File is present with contents of only root and occupancy. - ^D test should give same results both times! o Size of Driver.datafile is 16 bytes. o root and occupancy maintain values. blue is the color of the student name red is the color of the student number Inserting one item: ieng6.ucsd.edu% od -x Driver.datafile b ff

7 Inserting to the left and right of root: Match underlined, italicized and bold offsets: ieng6.ucsd.edu% od -x Driver.datafile b ff fff a5a 5a5a 5a5a 5a5a 5a5a 5a5a 5a5a 005a ffff View a deleted Node: ieng6.ucsd.edu% od -x Driver.datafile fff ffff ffff ffff ffff fff a5a 5a5a 5a5a 5a5a 5a5a 5a5a 5a5a 005a ffff Bold Italicized TNode is in the file but not in the Tree!

8 A new test of your Driver begins with make fresh - make clean, make new also start fresh. Testing Driver again without a make fresh : - Not a new test data is still there from old test. To run sample: cd ~ touch Driver.datafile../public/hw9/Driver rm Driver.datafile touch Calc.datafile../public/hw9/Calc rm Calc.datafile - You don t have permissions to create files in the public area. o Driver program will appear broken if run from public. Advice: - You ll want to check your file pointer for validity at the beginning of each method: if (!*fio) cerr << fio is corrupt in Tree s Insert!\n ; Possible reasons for fio corruption: 1. Writing. 2. Reading.

9 Cost: - Measures efficiency by tracking work: o Unit of Work is one Slower component of your system. Much slower than memory access. Operations: - Counts operations requested by user. o Inserts, Lookup, Remove of Tree. - Used to compute average cost. Cost of operations: 84 tree accesses: Number of operations: 17 Average cost: tree accesses/operation Logistics: Partners are allowed: One or two person submissions are allowed

10 Week Eight, Discussion Two: Syntax for fio s read and write: fio->read (param1, param2); - param1: the address in memory that is the destination of the information from the disk. - param2: how many bytes to read. - How: reading from disk begins at the current position of the g pointer. o Therefore, call before calling. fio->write (param1, param2); - param1: the address in memory that is the source of the information to go to disk. - param2: how many bytes to write. - How: writing to disk begins at the current position of the p pointer. o Therefore, call before calling. Levels of abstraction: Please maintain appropriate layers of abstraction in your code: - Example: No direct calls to disk accessing methods from Tree/TNode s Insert, Lookup, Remove, RARM. o Direct calls to disk accessing methods will be in.

11 To work on binary file aspect of the assignment, one update to Driver.c is required: 1. The name of the datafile needs to be passed to the SymTab constructor.: hw8: hw9: SymTab<UCSDStudent> ST; SymTab<UCSDStudent> ST ( ); Once this one update is done, then the hw8 Driver.c will work on hw9 s Tree on disk. - Completing ASCII file input part of the assignment is not necessary in order to complete the binary file part of the assignment. TNode constructor will call TNode s Read and TNode s Write methods - TNode s Read and Write will call fio->read and fio->write field-by-field o They will work all : reading or writing. Tree constructor assistance: Tree<Whatever> :: Tree (const char * datafile) : fio (new fstream (datafile, ios :: out ios :: in) { }

12 hw8 to hw9 translation: One line of code in hw8 translates to two lines in hw9: Example: left->insert (a, b, c); // hw8 TNode<Whatever> lefttnode (left, fio); lefttnode.insert (a, b, c); // hw9 To get started: 1. copy hw8 bodies into hw9 bodies. 2. translate each hw8 body into a hw9 body. 3. return 0 or return in empty bodies. 4. implement TNode constructors and Write/Read methods. 5. review/update UCSDStudent class. 6. add parameter to SymTab/Tree constructor. 7. implement Tree constructor/destructor. 8. test constructor/insert/write methods (following testing guide).