What is CreateFileMapping?
The CreateFileMapping function returns a handle to the file mapping object. This handle will be used when creating a file view so that you can access the shared memory.
Does MMAP work on Windows?
Windows doesn’t have mmap , but it does have MapViewOfFile . Both of these implement memory mapped files, but there’s one important difference: Windows keeps a lock on the file, not allowing it to be deleted. Even with the Windows flag FILE_SHARE_DELETE deletion does not work.
What is shared memory in windows?
In computer science, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Shared memory is an efficient means of passing data between programs.
What is memory mapped files and how in use?
A memory-mapped file contains the contents of a file in virtual memory. This mapping between a file and memory space enables an application, including multiple processes, to modify the file by reading and writing directly to the memory.
What does file locked with only readers mean?
Hi, STATUS_FILE_LOCKED_WITH_ONLY_READERS indicates that the file was locked and all users of the file can only read. And in fact, this is a successful code, because section data is prevented from changing while the lock is held.
What does mmap actually do?
In computing, mmap(2) is a POSIX-compliant Unix system call that maps files or devices into memory. It is a method of memory-mapped file I/O. It implements demand paging because file contents are not read from disk directly and initially do not use physical RAM at all.
What is shared memory in C?
Inter Process Communication through shared memory is a concept where two or more process can access the common memory. And communication is done via this shared memory where changes made by one process can be viewed by another process.
Is shared memory thread safe?
The issued of sharing data between threads are mostly due to the consequences of modifying data. If the data we share is read-only data, there will be no problem, because the data read by one thread is unaffected by whether or not another thread is reading the same data.
What is memory mapping in C?
This means reading or writing to those areas of memory causes the file to be read or written. This is the default mapping type. Anonymous mapping − This mapping maps the area of the process’ virtual memory without backed by any file. The contents are initialized to zero.
How does mmap work in C?
mmap works by manipulating your process’s page table, a data structure your CPU uses to map address spaces. The CPU will translate “virtual” addresses to “physical” ones, and does so according to the page table set up by your kernel. When you access the mapped memory for the first time, your CPU generates a page fault.
What is the return value of openfilemapping?
If the function succeeds, the return value is an open handle to the specified file mapping object. If the function fails, the return value is NULL. To get extended error information, call GetLastError. The handle that OpenFileMapping returns can be used with any function that requires a handle to a file mapping object.
What happens when openfilemapping fails to work?
If the function fails, the return value is NULL. To get extended error information, call GetLastError. The handle that OpenFileMapping returns can be used with any function that requires a handle to a file mapping object. When modifying a file through a mapped view, the last modification timestamp may not be updated automatically.
What is CreateFileMapping in MSDN?
MSDN: CreateFileMapping function Mapped views of a file mapping object maintain internal references to the object, and a file mapping object does not close until all references to it are released.
Is it possible to call CreateFileMapping in any order?
These functions can be called in any order. The CreateFileMapping documentation says that to fully close a file all handles must be closed and the order does not matter. This logic is not invertible: you cannot close a handle and expect to use the other handles as if the file mapping wasn’t ‘closed’.