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POWhat settings in my mmap code sets all the files data to zero?
 

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  1. POWhat settings in my mmap code sets all the files data to zero?
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    <p>I am implementing one half of a stream where you should be able to jump X integers back or forth. On top of that when I open a file it should preserve the data in the file. In this implementation I try to use mmap. My problem is when I open a file a second time the mapped data is purely zeroes. My open method is called createStream and looks like this:</p> <pre><code>void MapperOutForward::createStream(const char* filename) { this-&gt;filename = filename; pFile = open(filename, O_RDWR | O_CREAT | O_SYNC, S_IRWXG|S_IRWXO|S_IRWXU); if ( pFile == -1) { int errsv = errno; cout &lt;&lt; "MappedStreamOut createStream open error: " &lt;&lt; strerror( errno ) &lt;&lt; endl; } //getting file size and making the file big enough struct stat filestatus; stat( filename, &amp;filestatus ); if(filestatus.st_size &lt; mapSize + 1) { lseek (pFile, mapSize + 1, SEEK_SET); write (pFile, "", 1); } lseek (pFile, 0, SEEK_SET); map = (int*) mmap (0, mapSize, PROT_WRITE | PROT_READ, MAP_PRIVATE, pFile, 0); close (pFile); if ( map == (int*) -1) { cout &lt;&lt; "MappedStreamOut createStream mmap error: " &lt;&lt; strerror(errno) &lt;&lt; endl; } numberOfOffsets = 1; numberOfElementsInMap = 0; cout &lt;&lt; "Kopirer 5 før og 4 efter i Create" &lt;&lt; endl; for(int i = 0; i &lt; numberOfElementsInMap + 5; i++) { cout &lt;&lt; map[i] &lt;&lt; endl; } cout &lt;&lt; "Create numberOfOffsets:numberOfElementsInMap " &lt;&lt; numberOfOffsets &lt;&lt; ":" &lt;&lt; numberOfElementsInMap &lt;&lt; endl; } </code></pre> <p>The output at the end tells me that when I am done opening I am at the beginning of the file and the first 5 integers are 0. </p> <p>The O_CREAT flag in the open command should only create a file if it is not existing, and I can se that the file keeps its size after I call this command a second time. <a href="http://linux.die.net/man/2/open" rel="nofollow">man open</a></p> <p>The PROT_WRITE | PROT_READ flags in the mmap command seems only to activate some security and not changing anything in the file. <a href="http://linux.die.net/man/2/mmap" rel="nofollow">man mmap</a></p> <p>The rest of the class is here:</p> <pre><code>#include "MapperOutForward.h" using namespace std; #include &lt;cstdlib&gt; #include &lt;iostream&gt; #include &lt;fcntl.h&gt; #include &lt;sys/stat.h&gt; #include &lt;cmath&gt; MapperOutForward::MapperOutForward(int mapSize) //number of pages { pageSize = getpagesize(); this-&gt;mapSize = mapSize * pageSize; //we work in pages numberOfElementsInMap = 0; numberOfOffsets = 0; } MapperOutForward::~MapperOutForward() { munmap(map, mapSize); } void MapperOutForward::createStream(const char* filename) { this-&gt;filename = filename; pFile = open(filename, O_RDWR | O_CREAT | O_SYNC, S_IRWXG|S_IRWXO|S_IRWXU); if ( pFile == -1) { int errsv = errno; cout &lt;&lt; "MappedStreamOut createStream open error: " &lt;&lt; strerror( errno ) &lt;&lt; endl; } //getting file size and making the file big enough struct stat filestatus; stat( filename, &amp;filestatus ); if(filestatus.st_size &lt; mapSize + 1) { lseek (pFile, mapSize + 1, SEEK_SET); write (pFile, "", 1); } lseek (pFile, 0, SEEK_SET); map = (int*) mmap (0, mapSize, PROT_WRITE | PROT_READ, MAP_PRIVATE, pFile, 0); close (pFile); if ( map == (int*) -1) { cout &lt;&lt; "MappedStreamOut createStream mmap error: " &lt;&lt; strerror(errno) &lt;&lt; endl; } numberOfOffsets = 1; numberOfElementsInMap = 0; cout &lt;&lt; "Kopirer 5 før og 4 efter i Create" &lt;&lt; endl; for(int i = 0; i &lt; numberOfElementsInMap + 5; i++) { cout &lt;&lt; map[i] &lt;&lt; endl; } cout &lt;&lt; "Create numberOfOffsets:numberOfElementsInMap " &lt;&lt; numberOfOffsets &lt;&lt; ":" &lt;&lt; numberOfElementsInMap &lt;&lt; endl; } void MapperOutForward::writeNext(int* data, int numberOfElements) { for(int i = 0; i &lt; numberOfElements; i++) { writeHelper(data[i]); } cout &lt;&lt; "Kopirer 5 før og 4 efter i writeNext" &lt;&lt; endl; for(int i = numberOfElementsInMap - 5; i &lt; numberOfElementsInMap + 5; i++) { cout &lt;&lt; map[i] &lt;&lt; endl; } //cout &lt;&lt; "WriteNext numberOfOffsets:numberOfElementsInMap " &lt;&lt; numberOfOffsets &lt;&lt; ":" &lt;&lt; numberOfElementsInMap &lt;&lt; endl; } void MapperOutForward::writeHelper(int data) { int sizeOfInt = 4; //bytes if(numberOfElementsInMap &gt;= mapSize / sizeOfInt) //We need to create the next part of the file { munmap(map, mapSize); pFile = open(filename, O_RDWR | O_CREAT | O_SYNC, S_IRWXG|S_IRWXO|S_IRWXU); if ( pFile == -1) { std::cout&lt;&lt;"filename: "&lt;&lt;filename&lt;&lt;std::endl; std::cout&lt;&lt;"mapSize: "&lt;&lt;mapSize&lt;&lt;std::endl; int errsv = errno; cout &lt;&lt; "MappedStreamOut writeNext open error: " &lt;&lt; strerror( errno ) &lt;&lt; endl; } numberOfOffsets++; //Make the file bigger lseek (pFile, mapSize * numberOfOffsets, SEEK_SET); write (pFile, "", 1); lseek (pFile, 0, SEEK_SET); map = (int*) mmap (0, mapSize, PROT_WRITE | PROT_READ, MAP_PRIVATE, pFile, mapSize * (numberOfOffsets - 1)); close (pFile); if ( map == (int*) -1) { cout &lt;&lt; "MappedStreamOut writeNext mmap error: " &lt;&lt; strerror(errno) &lt;&lt; endl; } numberOfElementsInMap = 0; } map[numberOfElementsInMap] = data; numberOfElementsInMap++; } void MapperOutForward::jumpTo(int offset) { int sizeOfInt = 4; //bytes //cout &lt;&lt; "numberOfElementsInMap + offset " &lt;&lt; numberOfElementsInMap + offset &lt;&lt; endl; //cout &lt;&lt; "mapSize / sizeOfInt " &lt;&lt; mapSize / sizeOfInt &lt;&lt; endl; if(numberOfElementsInMap + offset &gt;= mapSize / sizeOfInt) { munmap(map, mapSize); pFile = open(filename, O_RDWR | O_CREAT | O_SYNC, S_IRWXG|S_IRWXO|S_IRWXU); if ( pFile == -1) { std::cout&lt;&lt;"filename: "&lt;&lt;filename&lt;&lt;std::endl; std::cout&lt;&lt;"mapSize: "&lt;&lt;mapSize&lt;&lt;std::endl; int errsv = errno; cout &lt;&lt; "MappedStreamOut writeNext open error: " &lt;&lt; strerror( errno ) &lt;&lt; endl; } numberOfOffsets += (int) ceil( (double) (numberOfElementsInMap + offset - (mapSize / sizeOfInt)) / (mapSize / sizeOfInt)); // rundet op ((resterende antal ints ud over mapSize) / (Antal ints i en mapsize)) = Antal offsets der skal springes //Make the file bigger lseek (pFile, mapSize * numberOfOffsets, SEEK_SET); write (pFile, "", 1); lseek (pFile, 0, SEEK_SET); map = (int*) mmap (0, mapSize, PROT_WRITE | PROT_READ, MAP_PRIVATE, pFile, mapSize * (numberOfOffsets - 1)); close (pFile); if ( map == (int*) -1) { cout &lt;&lt; "MappedStreamOut writeNext mmap error: " &lt;&lt; strerror(errno) &lt;&lt; endl; } numberOfElementsInMap = (numberOfElementsInMap + offset - (mapSize / sizeOfInt)) % (mapSize / sizeOfInt); //(resterende antal ints ud over mapSize) % (Antal ints i en mapsize) = Antal elementer ind i offsettet //cout &lt;&lt; "JumpTo offsetForward numberOfOffsets:numberOfElementsInMap " &lt;&lt; numberOfOffsets &lt;&lt; ":" &lt;&lt; numberOfElementsInMap &lt;&lt; endl; } else if(numberOfElementsInMap + offset &lt; 0) { munmap(map, mapSize); pFile = open(filename, O_RDWR | O_CREAT | O_SYNC, S_IRWXG|S_IRWXO|S_IRWXU); if ( pFile == -1) { std::cout&lt;&lt;"filename: "&lt;&lt;filename&lt;&lt;std::endl; std::cout&lt;&lt;"mapSize: "&lt;&lt;mapSize&lt;&lt;std::endl; int errsv = errno; cout &lt;&lt; "MappedStreamOut writeNext open error: " &lt;&lt; strerror( errno ) &lt;&lt; endl; } numberOfOffsets += (int) floor( (double) (numberOfElementsInMap + offset) / (mapSize / sizeOfInt)); // rundet op ((resterende antal ints ud over mapSize) / (Antal ints i en mapsize)) = Antal offsets der skal springes //Make the file bigger lseek (pFile, mapSize * numberOfOffsets, SEEK_SET); write (pFile, "", 1); lseek (pFile, 0, SEEK_SET); map = (int*) mmap (0, mapSize, PROT_WRITE | PROT_READ, MAP_PRIVATE, pFile, mapSize * (numberOfOffsets - 1)); close (pFile); if ( map == (int*) -1) { cout &lt;&lt; "MappedStreamOut writeNext mmap error: " &lt;&lt; strerror(errno) &lt;&lt; endl; } numberOfElementsInMap = (mapSize + (numberOfElementsInMap + offset)) % (mapSize / sizeOfInt); //(resterende antal ints ud over mapSize) % (Antal ints i en mapsize) = Antal elementer ind i offsettet //cout &lt;&lt; "JumpTo offsetBacward numberOfOffsets:numberOfElementsInMap " &lt;&lt; numberOfOffsets &lt;&lt; ":" &lt;&lt; numberOfElementsInMap &lt;&lt; endl; } else { numberOfElementsInMap += offset; //cout &lt;&lt; "JumpTo else numberOfOffsets:numberOfElementsInMap " &lt;&lt; numberOfOffsets &lt;&lt; ":" &lt;&lt; numberOfElementsInMap &lt;&lt; endl; } } void MapperOutForward::closeStream() { munmap(map, mapSize); } </code></pre> <p>And the main file is here:</p> <pre><code>#include "MapperInForward.h" #include "MapperOutForward.h" //#include "MapperOutBackward.h" //#include "MapperInBackward.h" //#include "MapperStreamFactory.h" #include &lt;functional&gt; int main( int argc, const char* argv[] ) { /*********************Tester Buffer Stream*************************************/ close(open((char*) "mapperTest", O_WRONLY | O_CREAT | O_SYNC | O_TRUNC, S_IRWXG|S_IRWXO|S_IRWXU)); //BufferStreamFactory* bsf = new BufferStreamFactory(3); MapperOutForward* mso = new MapperOutForward(1); mso-&gt;createStream((char*) "mapperTest"); int data[4000]; for(int i = 0; i &lt; 4000; i++) { data[i] = i + 1; } mso-&gt;writeNext(data, 4000); mso-&gt;closeStream(); MapperOutForward* mso1 = new MapperOutForward(1); mso1-&gt;createStream((char*) "mapperTest"); data[0] = 9999; mso1-&gt;jumpTo(0); mso1-&gt;jumpTo(100); mso1-&gt;writeNext(data, 1); mso1-&gt;jumpTo(1000); mso1-&gt;writeNext(data, 1); mso1-&gt;jumpTo(-900); mso1-&gt;writeNext(data, 1); mso1-&gt;closeStream(); } </code></pre> <p>It is all running on Ubuntu Linux and compiled with g++.</p> <p>Thanks for the time used to read all this and I hope you can help me. </p>
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