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reqrep.h  view on Meta::CPAN

    size_t         mmap_size;
    uint32_t       req_cap;
    uint32_t       req_cap_mask;  /* req_cap - 1 */
    uint32_t       req_arena_cap;
    uint32_t       resp_slots;
    uint32_t       resp_data_max;
    uint32_t       resp_stride;
    char          *copy_buf;
    uint32_t       copy_buf_cap;
    char          *path;
    int            notify_fd;     /* request notification eventfd, -1 if unset */
    int            reply_fd;      /* reply notification eventfd, -1 if unset */
    int            backing_fd;    /* memfd fd, -1 for file-backed/anonymous */
} ReqRepHandle;

/* ================================================================
 * Utility
 * ================================================================ */

static inline uint32_t reqrep_next_pow2(uint32_t v) {
    if (v < 2) return 2;
    if (v > 0x80000000U) return 0;
    v--;
    v |= v >> 1; v |= v >> 2; v |= v >> 4; v |= v >> 8; v |= v >> 16;
    return v + 1;
}

static inline void reqrep_spin_pause(void) {
#if defined(__x86_64__) || defined(__i386__)
    __asm__ volatile("pause" ::: "memory");
#elif defined(__aarch64__)
    __asm__ volatile("yield" ::: "memory");
#else
    __asm__ volatile("" ::: "memory");
#endif
}

static inline int reqrep_ensure_copy_buf(ReqRepHandle *h, uint32_t needed) {
    if (needed <= h->copy_buf_cap) return 1;
    uint32_t ns = h->copy_buf_cap ? h->copy_buf_cap : 64;
    while (ns < needed) { uint32_t n2 = ns * 2; if (n2 <= ns) { ns = needed; break; } ns = n2; }
    char *nb = (char *)realloc(h->copy_buf, ns);
    if (!nb) return 0;
    h->copy_buf = nb;
    h->copy_buf_cap = ns;
    return 1;
}

static inline RespSlotHeader *reqrep_resp_slot(ReqRepHandle *h, uint32_t idx) {
    return (RespSlotHeader *)(h->resp_area + (uint64_t)idx * h->resp_stride);
}

/* ================================================================
 * Futex helpers
 * ================================================================ */

#define REQREP_MUTEX_WRITER_BIT 0x80000000U
#define REQREP_MUTEX_PID_MASK   0x7FFFFFFFU
#define REQREP_MUTEX_VAL(pid)   (REQREP_MUTEX_WRITER_BIT | ((uint32_t)(pid) & REQREP_MUTEX_PID_MASK))

static inline int reqrep_pid_alive(uint32_t pid) {
    if (pid == 0) return 1;
    return !(kill((pid_t)pid, 0) == -1 && errno == ESRCH);
}

static const struct timespec reqrep_lock_timeout = { REQREP_LOCK_TIMEOUT_SEC, 0 };

static inline void reqrep_recover_stale_mutex(ReqRepHeader *hdr, uint32_t observed) {
    if (!__atomic_compare_exchange_n(&hdr->mutex, &observed, 0,
            0, __ATOMIC_ACQ_REL, __ATOMIC_RELAXED))
        return;
    __atomic_add_fetch(&hdr->stat_recoveries, 1, __ATOMIC_RELAXED);
    if (__atomic_load_n(&hdr->mutex_waiters, __ATOMIC_RELAXED) > 0)
        syscall(SYS_futex, &hdr->mutex, FUTEX_WAKE, 1, NULL, NULL, 0);
}

static inline void reqrep_mutex_lock(ReqRepHeader *hdr) {
    uint32_t mypid = REQREP_MUTEX_VAL((uint32_t)getpid());
    for (int spin = 0; ; spin++) {
        uint32_t expected = 0;
        if (__atomic_compare_exchange_n(&hdr->mutex, &expected, mypid,
                1, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
            return;
        if (__builtin_expect(spin < REQREP_SPIN_LIMIT, 1)) {
            reqrep_spin_pause();
            continue;
        }
        __atomic_add_fetch(&hdr->mutex_waiters, 1, __ATOMIC_RELAXED);
        uint32_t cur = __atomic_load_n(&hdr->mutex, __ATOMIC_RELAXED);
        if (cur != 0) {
            long rc = syscall(SYS_futex, &hdr->mutex, FUTEX_WAIT, cur,
                              &reqrep_lock_timeout, NULL, 0);
            if (rc == -1 && errno == ETIMEDOUT) {
                __atomic_sub_fetch(&hdr->mutex_waiters, 1, __ATOMIC_RELAXED);
                uint32_t val = __atomic_load_n(&hdr->mutex, __ATOMIC_RELAXED);
                if (val >= REQREP_MUTEX_WRITER_BIT) {
                    uint32_t pid = val & REQREP_MUTEX_PID_MASK;
                    if (!reqrep_pid_alive(pid))
                        reqrep_recover_stale_mutex(hdr, val);
                }
                spin = 0;
                continue;
            }
        }
        __atomic_sub_fetch(&hdr->mutex_waiters, 1, __ATOMIC_RELAXED);
        spin = 0;
    }
}

static inline void reqrep_mutex_unlock(ReqRepHeader *hdr) {
    __atomic_store_n(&hdr->mutex, 0, __ATOMIC_RELEASE);
    if (__atomic_load_n(&hdr->mutex_waiters, __ATOMIC_RELAXED) > 0)
        syscall(SYS_futex, &hdr->mutex, FUTEX_WAKE, 1, NULL, NULL, 0);
}

static inline void reqrep_wake_consumers(ReqRepHeader *hdr) {
    if (__atomic_load_n(&hdr->recv_waiters, __ATOMIC_RELAXED) > 0) {
        __atomic_add_fetch(&hdr->recv_futex, 1, __ATOMIC_RELEASE);
        syscall(SYS_futex, &hdr->recv_futex, FUTEX_WAKE, 1, NULL, NULL, 0);
    }
}

static inline void reqrep_wake_producers(ReqRepHeader *hdr) {
    if (__atomic_load_n(&hdr->send_waiters, __ATOMIC_RELAXED) > 0) {
        __atomic_add_fetch(&hdr->send_futex, 1, __ATOMIC_RELEASE);
        syscall(SYS_futex, &hdr->send_futex, FUTEX_WAKE, 1, NULL, NULL, 0);
    }
}

static inline void reqrep_wake_slot_waiters(ReqRepHeader *hdr) {
    if (__atomic_load_n(&hdr->slot_waiters, __ATOMIC_RELAXED) > 0) {
        __atomic_add_fetch(&hdr->slot_futex, 1, __ATOMIC_RELEASE);
        syscall(SYS_futex, &hdr->slot_futex, FUTEX_WAKE, 1, NULL, NULL, 0);
    }
}

static inline int reqrep_remaining_time(const struct timespec *deadline,
                                         struct timespec *remaining) {
    struct timespec now;
    clock_gettime(CLOCK_MONOTONIC, &now);
    remaining->tv_sec = deadline->tv_sec - now.tv_sec;
    remaining->tv_nsec = deadline->tv_nsec - now.tv_nsec;
    if (remaining->tv_nsec < 0) {
        remaining->tv_sec--;
        remaining->tv_nsec += 1000000000L;
    }
    return remaining->tv_sec >= 0;
}

static inline void reqrep_make_deadline(double timeout, struct timespec *deadline) {
    clock_gettime(CLOCK_MONOTONIC, deadline);
    deadline->tv_sec += (time_t)timeout;
    deadline->tv_nsec += (long)((timeout - (double)(time_t)timeout) * 1e9);
    if (deadline->tv_nsec >= 1000000000L) {
        deadline->tv_sec++;
        deadline->tv_nsec -= 1000000000L;
    }
}

/* ================================================================
 * Response slot operations
 * ================================================================ */

static int32_t reqrep_slot_acquire(ReqRepHandle *h) {
    uint32_t n = h->resp_slots;
    uint32_t hint = __atomic_load_n(&h->hdr->resp_hint, __ATOMIC_RELAXED);
    uint32_t mypid = (uint32_t)getpid();

    for (uint32_t i = 0; i < n; i++) {
        uint32_t idx = (hint + i) % n;
        RespSlotHeader *slot = reqrep_resp_slot(h, idx);
        uint32_t expected = RESP_FREE;
        if (__atomic_compare_exchange_n(&slot->state, &expected, RESP_ACQUIRED,
                0, __ATOMIC_ACQ_REL, __ATOMIC_RELAXED)) {
            __atomic_store_n(&slot->owner_pid, mypid, __ATOMIC_RELAXED);
            __atomic_add_fetch(&slot->generation, 1, __ATOMIC_RELEASE);
            __atomic_store_n(&h->hdr->resp_hint, (idx + 1) % n, __ATOMIC_RELAXED);
            return (int32_t)idx;
        }
    }

    /* Recover stale slots from dead processes (both ACQUIRED and READY) */
    for (uint32_t i = 0; i < n; i++) {
        RespSlotHeader *slot = reqrep_resp_slot(h, i);
        uint32_t state = __atomic_load_n(&slot->state, __ATOMIC_ACQUIRE);
        if (state == RESP_ACQUIRED || state == RESP_READY) {
            uint32_t pid = __atomic_load_n(&slot->owner_pid, __ATOMIC_RELAXED);
            if (pid && !reqrep_pid_alive(pid)) {
                if (__atomic_compare_exchange_n(&slot->state, &state, RESP_FREE,
                        0, __ATOMIC_ACQ_REL, __ATOMIC_RELAXED)) {
                    __atomic_add_fetch(&h->hdr->stat_recoveries, 1, __ATOMIC_RELAXED);
                    uint32_t expected = RESP_FREE;
                    if (__atomic_compare_exchange_n(&slot->state, &expected, RESP_ACQUIRED,
                            0, __ATOMIC_ACQ_REL, __ATOMIC_RELAXED)) {
                        __atomic_store_n(&slot->owner_pid, mypid, __ATOMIC_RELAXED);
                        __atomic_add_fetch(&slot->generation, 1, __ATOMIC_RELEASE);
                        return (int32_t)i;
                    }
                    reqrep_wake_slot_waiters(h->hdr);
                }
            }
        }
    }

    return -1;
}

static inline void reqrep_slot_release(ReqRepHandle *h, uint32_t idx) {
    RespSlotHeader *slot = reqrep_resp_slot(h, idx);
    __atomic_store_n(&slot->owner_pid, 0, __ATOMIC_RELAXED);
    __atomic_store_n(&slot->state, RESP_FREE, __ATOMIC_RELEASE);
    reqrep_wake_slot_waiters(h->hdr);
}

/* ================================================================
 * Create / Open / Close
 * ================================================================ */

#define REQREP_ERR(fmt, ...) do { if (errbuf) snprintf(errbuf, REQREP_ERR_BUFLEN, fmt, ##__VA_ARGS__); } while(0)

static ReqRepHandle *reqrep_setup_handle(void *base, size_t map_size,
                                          const char *path, int backing_fd) {
    ReqRepHeader *hdr = (ReqRepHeader *)base;
    ReqRepHandle *h = (ReqRepHandle *)calloc(1, sizeof(ReqRepHandle));
    if (!h) return NULL;

    h->hdr           = hdr;
    h->req_slots     = (ReqSlot *)((char *)base + hdr->req_slots_off);
    h->req_arena     = (char *)base + hdr->req_arena_off;
    h->resp_area     = (uint8_t *)base + hdr->resp_off;
    h->mmap_size     = map_size;
    h->req_cap       = hdr->req_cap;
    h->req_cap_mask  = hdr->req_cap - 1;
    h->req_arena_cap = hdr->req_arena_cap;
    h->resp_slots    = hdr->resp_slots;
    h->resp_data_max = hdr->resp_data_max;
    h->resp_stride   = hdr->resp_stride;
    h->path          = path ? strdup(path) : NULL;
    h->notify_fd     = -1;
    h->reply_fd      = -1;
    h->backing_fd    = backing_fd;

    return h;
}

static int reqrep_validate_header(ReqRepHeader *hdr, size_t file_size, uint32_t expected_mode) {
    if (hdr->magic != REQREP_MAGIC) return 0;
    if (hdr->version != REQREP_VERSION) return 0;