Programming

I would look to the existing problem in a different way. The problem as stated intially is "formulating a faster technique for transfer of data from Shared Memory to a file" .
I would suggest to divide the shared memory into small segments and allow a pair of thread to read/write from each domain, in sync. Hence multiple threads operates on the data together but at mapped memory address. Each thread pointers should be intialized once to the domain bounday (addresses space). Once done a write thread of each process can write to a specific region incrementing a global resource each for itself. Meanwhile a read thread for each data division conditionally waits for the global variable to reach its max or upper domain limit. Once the event is initiated the write thread should conditionally wait for the variable to be initialized to the lower boud limit meanwhile the read thread should write the data to the file. Hence block I/O would be possible , which I think could be faster than the existing.
But however I do take an assumption that the order in which data has to writen to the file is immaterial.