libakerror/tests/err_threads_init.c

#include "akerror.h"
#include "err_capture.h"
#include "err_threads.h"
#include <errno.h>
#include <string.h>

/*
 * akerr_init() runs exactly once, no matter how many threads reach the library
 * at the same instant.
 *
 * This is the hardest of the three to get right, because initialization is
 * re-entrant: akerr_init() reserves the library's own status band and names its
 * own codes, and every one of those calls goes through a public entry point
 * that calls akerr_init() again. The guard against that recursion has to be
 * per-thread, or a second thread arriving mid-initialization would see the flag
 * the first thread raised on its way in and walk tables that are still being
 * built.
 *
 * Nothing in main() touches the library before the threads start, so the race
 * is real: whichever thread wins does the initializing, and the rest must block
 * until it is finished rather than proceed on half-built tables.
 *
 * What proves it ran once rather than several times: each thread reserves its
 * own status range as its first act. A second pass through akerr_init() would
 * memset the range table, so a reservation made by a thread that raced ahead
 * would silently vanish -- exactly the failure the pre-1.0.0 library had. After
 * the join, every thread's reservation must still be there, still attributed to
 * that thread.
 */

static int thread_range_base(int id)
{
    return 400000 + (id * 16);
}

static void *init_racer(void *raw)
{
    akerr_ThreadArg *arg = raw;
    akerr_ErrorContext *e;
    char owner[32];
    char name[32];
    int base = thread_range_base(arg->id);

    snprintf(owner, sizeof(owner), "init-thread-%d", arg->id);
    snprintf(name, sizeof(name), "Thread %d Error", arg->id);
    pthread_barrier_wait(arg->barrier);

    /* First touch of the library from this thread, and for one of them the
     * first touch in the process. */
    e = akerr_reserve_status_range(base, 16, owner);
    AKERR_TCHECK(arg, e == NULL);
    RELEASE_ERROR(e);

    e = akerr_register_status_name(owner, base, name);
    AKERR_TCHECK(arg, e == NULL);
    RELEASE_ERROR(e);

    /* The library's own band was reserved by whichever thread initialized, and
     * every thread must see it as taken -- including the one that did it. A
     * second initialization would have wiped the reservation and let this
     * through. */
    e = akerr_reserve_status_range(0, AKERR_RESERVED_STATUS_COUNT, owner);
    AKERR_TCHECK(arg, e != NULL);
    if ( e != NULL ) {
	AKERR_TCHECK(arg, e->status == AKERR_STATUS_RANGE_OVERLAP);
	AKERR_TCHECK(arg, strstr(e->message, AKERR_LIBRARY_OWNER) != NULL);
    }
    RELEASE_ERROR(e);

    /* The name tables are complete as seen from every thread: the library's own
     * codes, the generated errno names, and this thread's own registration. */
    AKERR_TCHECK(arg, strcmp(akerr_name_for_status(AKERR_VALUE, NULL),
			     "Value Error") == 0);
    AKERR_TCHECK(arg, strcmp(akerr_name_for_status(AKERR_NULLPOINTER, NULL),
			     "Null Pointer Error") == 0);
    AKERR_TCHECK(arg, strcmp(akerr_name_for_status(EACCES, NULL),
			     "Unknown Error") != 0);
    AKERR_TCHECK(arg, strcmp(akerr_name_for_status(base, NULL), name) == 0);

    /* And an error raised from this thread renders with a name, which is the
     * whole point of the tables being complete. */
    PREPARE_ERROR(errctx);
    ATTEMPT {
	FAIL_BREAK(errctx, AKERR_TYPE, "raised during init race by thread %d",
		   arg->id);
    } CLEANUP {
    } PROCESS(errctx) {
    } HANDLE(errctx, AKERR_TYPE) {
	AKERR_TCHECK(arg, strstr(errctx->stacktracebuf, "Type Error") != NULL);
    } FINISH_NORETURN(errctx);

    return NULL;
}

int main(void)
{
    /* Installed before anything initializes: akerr_init() only supplies the
     * default logger when this is still NULL. */
    akerr_log_method = &akerr_thread_logger;

    int failures = akerr_run_threads(&init_racer);
    AKERR_CHECK(failures == 0);

    /* Every thread's reservation survived the race, under its own owner. */
    for ( int id = 1; id <= AKERR_TEST_THREADS; id++ ) {
	char owner[32];
	char name[32];
	int base = thread_range_base(id);

	snprintf(owner, sizeof(owner), "init-thread-%d", id);
	snprintf(name, sizeof(name), "Thread %d Error", id);
	AKERR_CHECK(strcmp(akerr_name_for_status(base, NULL), name) == 0);
	AKERR_CHECK_RAISES(akerr_reserve_status_range(base, 16, "verifier"),
			   AKERR_STATUS_RANGE_OVERLAP);
	AKERR_CHECK_MESSAGE_CONTAINS(owner);
    }

    /* Nothing leaked a pool slot on the way through. */
    AKERR_CHECK(akerr_slots_in_use() == 0);

    fprintf(stderr, "err_threads_init ok (%d threads raced initialization)\n",
	    AKERR_TEST_THREADS);
    return 0;
}