Multithreaded input queue mode

By default, kdb+ is single-threaded, and processes incoming queries sequentially.

An additional mode exists, designed for serving in-memory static data to an externally constrained number of clients only; it is not intended for use as a gateway, or serving mutable data, or data from disk. Each incoming connection is executed in its own thread, and is unable to update globals – it is purely functional in the sense that the execution of a query should not have side-effects.

There can be a maximum of 1020 concurrent connections, with each connection requiring a minimum of 64MB, the real amount depending on the working space required by the query being executed. Each connection has its own thread, which is reading, calculating or writing a response. In addition, there is the main thread, which monitors stdin, invokes .z.ts on timer expiry and monitors other socket descriptors. (There should not be any).

Updates to globals are allowed only if they occur from within .z.ts, or via a socket listed in .z.W. Updates should not be frequent, as they wait for completion of exiting queries and block new queries (using multiple-read single-write lock), thus slowing processing speeds. If an attempt is made to update globals from threads other than main, a 'no update error is issued.

The switching in and out of this mode now checks to avoid the situation where the main thread could have a socket open, and sockets being processed in other threads simultaneously.

Multithreaded input queue mode is active when the port for incoming connections is specified as negative, e.g. for startup

$ q -p -5000