<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>monocasa</author><text>Writing a top level comment here to hopefully address some of the misconceptions present across this comment section.&lt;p&gt;Doors at the end of the day aren&amp;#x27;t message passing based RPC.  There is no door_recv(2) syscall or equivalent nor any way for a thread pool in the callee to wait for requests.&lt;p&gt;Doors at the end of the day are a control transfer primitive.  In a very real sense the calling thread is simply transferred to the callee&amp;#x27;s address space and continues execution there until a door_return(2) syscall transfers it back into the caller address_space.&lt;p&gt;It truly is a &amp;#x27;door&amp;#x27; into another address space.&lt;p&gt;This is most similar to some of the CPU control transfer primitives.  It&amp;#x27;s most like task gate style constructs like seen on 286&amp;#x2F;i432&amp;#x2F;mill CPUs.  Arguably it&amp;#x27;s kind of like the system call instruction itself too, transferring execution directly to another address space&amp;#x2F;context.</text><parent_chain></parent_chain></comment><story><title>&quot;Doors&quot; in Solaris: Lightweight RPC Using File Descriptors (1996)</title><url>http://www.kohala.com/start/papers.others/doors.html</url></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>robinhouston</author><text>Back in 1998 or so, a colleague and I were tasked with building a system to target adverts to particular users on a website. It obviously needed to run very efficiently, because it would be invoked on every page load and the server hardware of the time was very underpowered by today’s standards.&lt;p&gt;The Linux server revolution was still a few years away (at least it was for us – perhaps we were behind the curve), so our webservers were all Sun Enterprise machines running Solaris.&lt;p&gt;We decided to use a server process that had an in-memory representation of the active users, which we would query using doors from a custom Apache module. (I had read about doors and thought they sounded cool, but neither of us had used them before.)&lt;p&gt;It worked brilliantly and was extremely fast, though in the end it was never used in production because of changing business priorities.</text><parent_chain></parent_chain></comment><story><title>&quot;Doors&quot; in Solaris: Lightweight RPC Using File Descriptors (1996)</title><url>http://www.kohala.com/start/papers.others/doors.html</url></story>