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POMemory mapped file class, threads and reference counting
 

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    <p>I'm putting together a class I'm going to call a file.</p> <p>The file object simply contains a pointer to a memory mapped file and a link.</p> <p>The constructor takes a file and maps the file onto memory range. In summary it looks a bit like this:</p> <pre><code>class file { public: file(unsigned char* filename) { open(filename); } open(unsigned char* filename) { /// snip length_ = fstat(.....) file_ = mmap(.....) } private: unsigned int length_; unsigned char* bytes_; }; </code></pre> <p>Now, This file object can be copied around.</p> <p>Here comes the fun. Normally, a class like this would require a deep copy constructor to copy bytes_. However, I'm satisfied that I can just copy the pointer because the memory is shared and it should look at the same file anyway. I don't want to remap the file. But, obviously, to prevent a memory leak bytes_ at some point would need to be freed.</p> <p>What mechanisms can I use to decide when to delete the memory and munmap?</p> <p>I was thinking about using a boost::shared_ptr in order to free memory in the destructor only when it's the last reference, but I'd have to guard that with a mutex lock right? Are there some convenient boost functions for me to use already? I do not want to have to pull in another big library, it's not an option.</p> <p>i.e. </p> <pre><code>boost::shared_ptr&lt;unsigned char&gt; bytes_; ~file() { // enter some sort of critical section if (bytes_.unique()){ munmap(bytes_); bytes_ = 0; } // exit critical section } </code></pre>
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    1. COjust noticed. all class members are private.
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    2. COSee http://stackoverflow.com/questions/93073/how-to-implement-thread-safe-reference-counting-in-c
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