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Local Procedure Call Facility
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| bet | 9/13 | | Sana | 21.03.2017 | | Hajmi | 0.63 Mb. | | #1024 |
Local Procedure Call Facility. NT's Local Procedure Call (LPC) Facility optimizes communications for applications, including operating system environments. The LPC function is based on two types of port object: connection ports and communication ports. A server creates a connection port, which a client connects to. After the client establishes that connection, the server creates a communication port, which the server and client transmit data through.
Three kinds of LPC exist: data copying, shared memory, and shared memory with event pairs (Quick-LPC). NT uses data copying for small messages (less than 256 bytes). One end of the communications link (client or server) copies a message to a port, and the other end of the link copies the message out of the port.
NT uses shared memory for messages larger than 256 bytes. In shared-memory LPC, the connected client and server share a region of memory. When one end of the communications link wants to send a message larger than 256 bytes to the other, it sends through the communications port a short message whose only function is to point to the location of the primary message in the shared memory. Shared memory avoids a copy operation but requires dedicated shared memory. Win32 under NT 3.51 uses Quick-LPC. Win32 doesn't send messages through ports. Instead, one end of the communications link uses an event-pair synchronization object to signal the other end of the communications link that it has placed a message in shared memory. Using event-pair synchronization objects avoids the overhead of communicating through a port but as a trade-off has even higher resource overhead than other LPC methods.
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