src/runtime/gc-thread-pool.c

   1 #define _GNU_SOURCE
   2 #include <errno.h>
   3 #include <pthread.h>
   4 #include <stdlib.h>
   5 #include <semaphore.h>
   6 #include "interr.h"
   7
   8 static unsigned int gc_threads;
   9 static pthread_t *threads;
  10 static os_sem_t *start_semaphores;
  11 static os_sem_t join_semaphore;
  12 static void (*action)(void);
  13
  14 static void *worker(void *index) {
  15   uword_t i = (uword_t)index;
  16   while (1) {
  17     os_sem_wait(start_semaphores + i);
  18     // We don't need pthread_jit_write_protect_np(0) here because workers
  19     // never alter Lisp objects- they'll only touch side tables.
  20     // Though how does incremental compaction work? I guess _only_ the main thread
  21     // transports objects after marking is done?
  22     action();
  23     os_sem_post(&join_semaphore);
  24   }
  25   return NULL;
  26 }
  27
  28 void thread_pool_init() {
  29   char *str = getenv("GC_THREADS"), *tail;
  30   if (str == NULL) {
  31     gc_threads = 3;
  32   } else {
  33     unsigned long parse = strtoul(str, &tail, 10);
  34     if (tail == str || parse >= 256) lose("%s isn't a number of GC threads", str);
  35     gc_threads = parse;
  36   }
  37
  38 #ifdef LISP_FEATURE_DARWIN
  39   if (1) { // pre-existing semaphores aren't visible in a forked child
  40 #else
  41   if (!start_semaphores) {
  42 #endif
  43     start_semaphores = successful_malloc(sizeof(os_sem_t) * gc_threads);
  44     for (unsigned int i = 0; i < gc_threads; i++)
  45       os_sem_init(start_semaphores + i, 0);
  46     os_sem_init(&join_semaphore, 0);
  47   }
  48
  49   threads = successful_malloc(sizeof(pthread_t) * gc_threads);
  50   for (uword_t i = 0; i < gc_threads; i++)
  51     if (pthread_create(threads + i, NULL, worker, (void*)i))
  52       lose("Failed to create GC thread #%ld", i);
  53     else {
  54 #ifdef LISP_FEATURE_LINUX
  55       pthread_setname_np(threads[i], "Parallel GC");
  56 #endif
  57     }
  58 }
  59
  60 static void wake_gc_threads() {
  61   for (unsigned int i = 0; i < gc_threads; i++) os_sem_post(start_semaphores + i);
  62 }
  63
  64 static void join_gc_threads() {
  65   for (unsigned int i = 0; i < gc_threads; i++) os_sem_wait(&join_semaphore);
  66 }
  67
  68 void run_on_thread_pool(void (*act)(void)) {
  69   action = act;
  70   wake_gc_threads();
  71   act();
  72   join_gc_threads();
  73   action = 0; // tidy up
  74 }