pthread_create - glibc

Split from the chapter glibc: Process, Threads and Signals into the per-function layout; see the method page and the glibc ledger for coverage status.

Threads (NPTL)

Semantics – start a thread running start_routine(arg); store its pthread_t in *thread. attr == NULL means defaults. Inheriting rules: the new thread gets a copy of the creator’s signal mask, an empty pending-signal set, and does not inherit the alternate signal stack; it inherits the FP environment, capabilities and CPU affinity mask.

Error return convention (the interview trap) – returns 0 or an error number directly: it does not set errno and never returns -1. Errors: EAGAIN (resources or a system limit: RLIMIT_NPROC, threads-max, pid_max), EINVAL (bad attr), EPERM (sched policy not permitted). Set errno = s; perror(...) to report.

Attributes and stack size defaults – pthread_attr_t knobs: detachstate (default PTHREAD_CREATE_JOINABLE), scope, inheritsched, schedpolicy/param, guardsize (default one page, 4096), stackaddr/ stacksize. NPTL default stack: RLIMIT_STACK at program start if finite, else per-architecture (x86_64 2 MiB, i386 2 MiB, IA-64 32 MiB). Under _GNU_SOURCE/_DYNAMIC_STACK_SIZE_SOURCE (glibc 2.34), PTHREAD_STACK_MIN itself becomes sysconf(_SC_THREAD_STACK_MIN).

Edge cases – which thread runs first after creation is indeterminate (absent real-time scheduling); returning from start_routine is pthread_exit(return_value); pthread_equal compares IDs; pthread_self returns the caller’s.

Example

pthread_t t; int s = pthread_create(&t, NULL, worker, arg);
if (s != 0) { errno = s; perror("pthread_create"); }

References – pthread_create(3), pthread_attr_init(3), clone(2); manual Creating and Destroying Threads; syscall view: clone; model context: threads.