That is not a thread. Linux man clone right at the start … “clone, __clone2, clone3 - create a child process”
What you want is pthread_create (or similar) There’s a bunch of not well documented dragons if you’re trying to treat a child process as a thread. Use POSIX Threads, as pretty much anytime PG or anything else Linux based says thread they’re talking about a POSIX Thread environment. On Wed, May 3, 2023 at 05:12 Michael J. Baars < mjbaars1977.pgsql.hack...@gmail.com> wrote: > Hi Peter, > > The shared common address space is controlled by the clone(2) CLONE_VM > option. Indeed this results in an environment in which both the parent and > the child can read / write each other's memory, but dynamic memory being > allocated using malloc(3) from two different threads simulaneously will > result in internal interference. > > Because libpq makes use of malloc to store results, you will come to find > that the CLONE_VM option was not the option you were looking for. > > On Tue, 2 May 2023, 19:58 Peter J. Holzer, <hjp-pg...@hjp.at> wrote: > >> On 2023-05-02 17:43:06 +0200, Michael J. Baars wrote: >> > I don't think it is, but let me shed some more light on it. >> >> One possibly quite important information you haven't told us yet is >> which OS you use. >> >> Or how you create the threads, how you pass the results around, what >> else you are possibly doing between getting the result and trying to use >> it ... >> >> A short self-contained test case might shed some light on this. >> >> >> > After playing around a little with threads and memory, I now know that >> the >> > PGresult is not read-only, it is read-once. The child can only read that >> > portion of parent memory, that was written before the thread started. >> Read-only >> > is not strong enough. >> > >> > Let me correct my first mail. Making libpq use mmap is not good enough >> either. >> > Shared memory allocated by the child can not be accessed by the parent. >> >> Are you sure you are talking about threads and not processes? In the OSs >> I am familiar with, threads (of the same process) share a common address >> space. You don't need explicit shared memory and there is no such thing >> as "parent memory" (there is thread-local storage, but that's more a >> compiler/library construct). >> >> hp >> >> -- >> _ | Peter J. Holzer | Story must make more sense than reality. >> |_|_) | | >> | | | h...@hjp.at | -- Charles Stross, "Creative writing >> __/ | http://www.hjp.at/ | challenge!" >> > -- "Genius might be described as a supreme capacity for getting its possessors into trouble of all kinds." -- Samuel Butler
