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fdsel.h

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//
// fdsel - select-style file descriptor set management
//
#ifndef _H_FDSEL
#define _H_FDSEL

#include <security_utilities/utilities.h>
#include <sys/types.h>
#include <security_utilities/debugging.h>


namespace Security {
namespace UnixPlusPlus {


//
// An FDSet object maintains a single select(2) compatible bitmap.
// Size is implicitly kept by the caller (who needs to call grow() as
// needed, starting at zero). As long as this is done correctly, we are
// not bound by the FD_SETSIZE limit.
// An FDSet can self-copy for select(2) use; after that, the [] operator
// investigates the copy.
//
// Why are we using the FD_* macros even though we know these
// are fd_mask arrays? Some implementations use optimized assembly
// for these operations, and we want to pick those up.
//
// This whole mess is completely UNIX specific. If your system has
// the poll(2) system call, ditch this and use it.
//
class FDSet {
public:
    FDSet() : mBits(NULL), mUseBits(NULL) { }
    ~FDSet();

    void grow(int oldWords, int newWords);
    void set(int fd, bool on);
    
    fd_set *make(int words);
    bool operator [] (int fd) const { return FD_ISSET(fd, (fd_set *)mUseBits); }
    
    inline static int words(int fd) { return (fd - 1) / NFDBITS + 1; }

private:
    fd_mask *mBits;                             // base bits
    fd_mask *mUseBits;                    // mutable copy for select(2)
    
    void grow(fd_mask * &bits, int oldWords, int newWords);
};


}     // end namespace UnixPlusPlus
}     // end namespace Security


#endif //_H_FDSEL

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