Overview of the Shared Memory Model

In the shared memory model, an application process creates an RSM export segment from the process's local address space. One or more remote application processes create an RSM import segment with a virtual connection between export and import segments across the interconnect. All processes make memory references for the shared segment with addresses local to their specific address space.

An application process creates an RSM export segment by allocating locally addressable memory to the export segment. This allocation is done by using one of the standard Solaris interfaces, such as System V Shared Memory, mmap(2), or valloc(3C). The process then calls on the RSMAPI for the creation of a segment, which provides a reference handle for the allocated memory. The RSM segment is published through one or more interconnect controllers. A published segment is remotely accessible. A list of access privileges for the nodes that are permitted to import the segment is also published.

A segment ID is assigned to the exported segment. This segment ID, along with the cluster node ID of the creating process, allows an importing process to uniquely specify an export segment. Successfully creating an export segment returns a segment handle to the process for use in subsequent segment operations.

An application process obtains access to a published segment by using the RSMAPI to create an import segment. After creating the import segment, the application process forms a virtual connection across the interconnect. Successfully creating this import segment returns an RSM import segment handle to the application process for use in subsequent segment import operations. After establishing the virtual connection, the application might request RSMAPI to provide a memory map for local access, if supported by the interconnect. If memory mapping is not supported, the application can use memory access primitives provided by RSMAPI.

The RSMAPI provides a mechanism to support remote access error detection and to resolve write-order memory model issues. This mechanism is called a barrier.

RSMAPI provides a notification mechanism to synchronize local and remote accesses. An export process can call a function to block while an import process finishes a data write operation. When the import process finishes writing, the process unblocks the export process by calling a signal function. Once unblocked, the export process processes the data.