110 lines
3.0 KiB
C
110 lines
3.0 KiB
C
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#pragma once
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#include <atomic>
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#include <cstddef>
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#include <cstdint>
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#include <new>
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#include "libipc/def.h"
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#include "libipc/rw_lock.h"
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#include "libipc/platform/detail.h"
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namespace ipc {
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namespace circ {
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using u1_t = ipc::uint_t<8>;
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using u2_t = ipc::uint_t<32>;
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/** only supports max 32 connections in broadcast mode */
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using cc_t = u2_t;
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constexpr u1_t index_of(u2_t c) noexcept {
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return static_cast<u1_t>(c);
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}
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class conn_head_base {
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protected:
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std::atomic<cc_t> cc_{0}; // connections
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ipc::spin_lock lc_;
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std::atomic<bool> constructed_{false};
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public:
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void init() {
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/* DCLP */
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if (!constructed_.load(std::memory_order_acquire)) {
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IPC_UNUSED_ auto guard = ipc::detail::unique_lock(lc_);
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if (!constructed_.load(std::memory_order_relaxed)) {
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::new (this) conn_head_base;
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constructed_.store(true, std::memory_order_release);
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}
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}
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}
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conn_head_base() = default;
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conn_head_base(conn_head_base const &) = delete;
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conn_head_base &operator=(conn_head_base const &) = delete;
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cc_t connections(std::memory_order order = std::memory_order_acquire) const noexcept {
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return this->cc_.load(order);
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}
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};
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template <typename P, bool = relat_trait<P>::is_broadcast>
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class conn_head;
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template <typename P>
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class conn_head<P, true> : public conn_head_base {
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public:
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cc_t connect() noexcept {
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for (unsigned k = 0;; ipc::yield(k)) {
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cc_t curr = this->cc_.load(std::memory_order_acquire);
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cc_t next = curr | (curr + 1); // find the first 0, and set it to 1.
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if (next == 0) {
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// connection-slot is full.
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return 0;
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}
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if (this->cc_.compare_exchange_weak(curr, next, std::memory_order_release)) {
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return next ^ curr; // return connected id
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}
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}
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}
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cc_t disconnect(cc_t cc_id) noexcept {
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return this->cc_.fetch_and(~cc_id, std::memory_order_acq_rel) & ~cc_id;
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}
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std::size_t conn_count(std::memory_order order = std::memory_order_acquire) const noexcept {
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cc_t cur = this->cc_.load(order);
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cc_t cnt; // accumulates the total bits set in cc
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for (cnt = 0; cur; ++cnt) cur &= cur - 1;
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return cnt;
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}
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};
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template <typename P>
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class conn_head<P, false> : public conn_head_base {
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public:
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cc_t connect() noexcept {
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return this->cc_.fetch_add(1, std::memory_order_relaxed) + 1;
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}
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cc_t disconnect(cc_t cc_id) noexcept {
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if (cc_id == ~static_cast<circ::cc_t>(0u)) {
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// clear all connections
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this->cc_.store(0, std::memory_order_relaxed);
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return 0u;
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}
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else {
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return this->cc_.fetch_sub(1, std::memory_order_relaxed) - 1;
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}
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}
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std::size_t conn_count(std::memory_order order = std::memory_order_acquire) const noexcept {
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return this->connections(order);
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}
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};
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} // namespace circ
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} // namespace ipc
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