RWCacheManager

Module:  Essential Tools Module   Group:  File System Classes

Does not inherit

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• Synopsis
• Description
• Persistence
• Example
• Public Constructor
• Public Destructor
• Public Member Functions

Members

flush() invalidate()

read() RWCacheManager()

write() ~RWCacheManager()

#include <rw/cacheman.h>
RWFile f("file.dat");       // Construct a file
RWCacheManager(&f, 100);    // Cache 100 byte blocks 
                            // to file.dat

Class RWCacheManager caches fixed length blocks to and from an associated RWFile. The block size can be of any length and is set at construction time. The number of cached blocks can also be set at construction time.

Writes to the file may be deferred. Use member function flush() to have any pending writes performed.

None

#include <rw/cacheman.h>
#include <rw/rwfile.h>

struct Record {
  int i;
  float f;
  char str[15];
};

int main() {
   RWFile file("file.dat");     // Construct a file

   // Construct a cache, using 20 slots for struct Record:
   RWCacheManager cache(&file, sizeof(Record), 20);

   Record r;
   r.i = 1;
   r.f = 3.14f;
   r.str [0] = 0;

   // ...
   cache.write(0, &r);
   // ...
   cache.read(0, &r);

   return 0;
}

Program output: written to file file.dat

RWCacheManager(RWFile* file, unsigned blocksz, 
               unsigned mxblks = 10);

Construct a cache for the RWFile pointed to by file. The length of the fixed-size blocks is given by blocksz. The number of cached blocks is given by mxblks. If the total number of bytes cached would exceed the maximum value of an unsigned int, then RWCacheManager will quietly decide to cache a smaller number of blocks.

~RWCacheManager();

Performs any pending I/O operations (i.e., calls flush()) and deallocates any allocated memory.

bool
flush();

Perform any pending I/O operations. Returns true if the flush was successful, false otherwise.

void
invalidate();

Invalidate the cache.

bool
read(RWoffset locn, void* dat);

Return the data located at offset locn of the associated RWFile. The data is put in the buffer pointed to by dat. This buffer must be at least as long as the block size specified when the cache was constructed. Returns true if the operation was successful, otherwise false.

bool
write(RWoffset locn, void* dat);

Write the block of data pointed to by dat to the offset locn of the associated RWFile. The number of bytes written is given by the block size specified when the cache was constructed. The actual write to disk may be deferred. Use member function flush() to perform any pending output. Returns true if the operation was successful, otherwise false.

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