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优化版unsync.Mutex提升多goroutine互斥锁性能

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从给定的文件信息中,我们可以提取以下IT知识要点: 1. 并发编程中的互斥锁(Mutex): 在并发编程中,互斥锁是同步机制的基本组件,用于防止多个goroutine同时访问共享资源。互斥锁的目的是保证某一时刻只有一个goroutine能够执行特定代码块,从而防止资源竞争和不一致的数据状态。 2. Go语言的互斥锁sync.Mutex: Go语言内置的sync包提供了一个互斥锁的实现,即sync.Mutex。该互斥锁在使用时,调用者需要显式地锁定(Lock)和解锁(Unlock)它,以防止并发冲突。使用不当,如忘记解锁,会导致死锁问题。sync.Mutex适用于需要严格锁定和解锁控制的场景。 3. unsync.Mutex的提出与优化: 文件中提到的unsync.Mutex是一种针对特定情况进行了优化的互斥锁。根据提供的描述,unsync.Mutex在某些场景下避免了同步操作,这样可以在不影响数据一致性的前提下减少同步开销,提高性能。 4. 基准测试(Benchmarking): 基准测试是用来衡量代码执行性能的一种测试方法。通过在不同条件下执行相同的代码,可以比较不同实现的性能。在本文件中,提供了三种基准测试:使用sync.Mutex的标准互斥锁、始终同步的unsync.Mutex和不执行同步的unsync.Mutex。这些测试结果可以为我们提供关于不同互斥锁实现性能的直接比较。 5. 性能指标: 基准测试中涉及的性能指标主要是执行速度,这里用纳秒每操作(ns/op)表示。数值越低,表示执行速度越快。测试结果显示,unsync.Mutex在某些情况下可能比sync.Mutex更快。 6. 多核与超线程(Hyper-Threading): 在CPU的配置信息中提到了4个内核和8个超线程。这意味着每个物理CPU核心可以模拟出两个逻辑线程,从而提高处理能力。在并发测试中,更多的核心和线程能提供更接近实际应用场景的测试环境。 7. Go语言包管理与版本控制: 提到的“unsync-master”文件列表暗示了这是一个Go语言包,而且是该包的主分支或主版本。在Go语言中,通常通过go.mod文件来管理依赖,而master或main通常表示主分支,表明这是一个活跃的开发分支。 8. goroutine的概念: goroutine是Go语言并发模型的核心,它是一种轻量级的线程,由Go运行时管理。goroutine的创建和管理成本远低于传统的操作系统线程。它们使得并发编程更加高效和简单。在基准测试中,通过增加goroutine的数量,可以测试不同锁在并发下的性能表现。 9. 测试环境: 测试是在Linux操作系统、amd64架构下进行的,并且使用了特定型号的Intel处理器。硬件配置对测试结果有很大影响,因此在分析和比较基准测试结果时,需要考虑测试环境的差异。 以上这些知识点涵盖了从并发控制、性能测试,到Go语言特有的实现细节等多个方面。它们对于理解特定的编程语言特性和优化并发程序的性能至关重要。在实际开发中,合理选择和使用同步机制能够显著提升软件的性能和稳定性。

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int ntpd_main(int argc UNUSED_PARAM, char **argv) { #undef G struct globals G; struct pollfd *pfd; peer_t **idx2peer; unsigned cnt; memset(&G, 0, sizeof(G)); SET_PTR_TO_GLOBALS(&G); ntp_init(argv); /* If ENABLE_FEATURE_NTPD_SERVER, + 1 for listen_fd: */ cnt = G.peer_cnt + ENABLE_FEATURE_NTPD_SERVER; idx2peer = xzalloc(sizeof(idx2peer[0]) * cnt); pfd = xzalloc(sizeof(pfd[0]) * cnt); /* Countdown: we never sync before we sent INITIAL_SAMPLES+1 * packets to each peer. * NB: if some peer is not responding, we may end up sending * fewer packets to it and more to other peers. * NB2: sync usually happens using INITIAL_SAMPLES packets, * since last reply does not come back instantaneously. */ cnt = G.peer_cnt * (INITIAL_SAMPLES + 1); while (!bb_got_signal) { llist_t *item; unsigned i, j; int nfds, timeout; double nextaction; /* Nothing between here and poll() blocks for any significant time */ nextaction = G.last_script_run + (11*60); if (nextaction < G.cur_time + 1) nextaction = G.cur_time + 1; i = 0; #if ENABLE_FEATURE_NTPD_SERVER if (G_listen_fd != -1) { pfd[0].fd = G_listen_fd; pfd[0].events = POLLIN; i++; } #endif /* Pass over peer list, send requests, time out on receives */ for (item = G.ntp_peers; item != NULL; item = item->link) { peer_t *p = (peer_t *) item->data; if (p->next_action_time <= G.cur_time) { if (p->p_fd == -1) { /* Time to send new req */ if (--cnt == 0) { VERB4 bb_simple_error_msg("disabling burst mode"); G.polladj_count = 0; G.poll_exp = MINPOLL; } send_query_to_peer(p); } else { /* Timed out waiting for reply */ close(p->p_fd); p->p_fd = -1; /* If poll interval is small, increase it */ if (G.poll_exp < BIGPOLL) adjust_poll(MINPOLL); timeout = poll_interval(NOREPLY_INTERVAL); bb_error_msg("timed out waiting for %s, reach 0x%02x, next query in %us", p->p_dotted, p->reachable_bits, timeout); /* What if don't see it because it changed its IP? */ if (p->reachable_bits == 0) resolve_peer_hostname(p); set_next(p, timeout); } } if (p->next_action_time < nextaction) nextaction = p->next_action_time; if (p->p_fd >= 0) { /* Wait for reply from this peer */ pfd[i].fd = p->p_fd; pfd[i].events = POLLIN; idx2peer[i] = p; i++; } } timeout = nextaction - G.cur_time; if (timeout < 0) timeout = 0; timeout++; /* (nextaction - G.cur_time) rounds down, compensating */ /* Here we may block */ VERB2 { if (i > (ENABLE_FEATURE_NTPD_SERVER && G_listen_fd != -1)) { /* We wait for at least one reply. * Poll for it, without wasting time for message. * Since replies often come under 1 second, this also * reduces clutter in logs. */ nfds = poll(pfd, i, 1000); if (nfds != 0) goto did_poll; if (--timeout <= 0) goto did_poll; } bb_error_msg("poll:%us sockets:%u interval:%us", timeout, i, 1 << G.poll_exp); } nfds = poll(pfd, i, timeout * 1000); did_poll: gettime1900d(); /* sets G.cur_time */ if (nfds <= 0) { double ct; int dns_error; if (bb_got_signal) break; /* poll was interrupted by a signal */ if (G.cur_time - G.last_script_run > 11*60) { /* Useful for updating battery-backed RTC and such */ run_script("periodic", G.last_update_offset); gettime1900d(); /* sets G.cur_time */ } /* Resolve peer names to IPs, if not resolved yet. * We do it only when poll timed out: * this way, we almost never overlap DNS resolution with * "request-reply" packet round trip. */ dns_error = 0; ct = G.cur_time; for (item = G.ntp_peers; item != NULL; item = item->link) { peer_t *p = (peer_t *) item->data; if (p->next_action_time <= ct && !p->p_lsa) { /* This can take up to ~10 sec per each DNS query */ dns_error |= (!resolve_peer_hostname(p)); } } if (!dns_error) goto check_unsync; /* Set next time for those which are still not resolved */ gettime1900d(); /* sets G.cur_time (needed for set_next()) */ for (item = G.ntp_peers; item != NULL; item = item->link) { peer_t *p = (peer_t *) item->data; if (p->next_action_time <= ct && !p->p_lsa) { set_next(p, HOSTNAME_INTERVAL * p->dns_errors); } } goto check_unsync; } /* Process any received packets */ j = 0; #if ENABLE_FEATURE_NTPD_SERVER if (G.listen_fd != -1) { if (pfd[0].revents /* & (POLLIN|POLLERR)*/) { nfds--; recv_and_process_client_pkt(/*G.listen_fd*/); gettime1900d(); /* sets G.cur_time */ } j = 1; } #endif for (; nfds != 0 && j < i; j++) { if (pfd[j].revents /* & (POLLIN|POLLERR)*/) { /* * At init, alarm was set to 10 sec. * Now we did get a reply. * Increase timeout to 50 seconds to finish syncing. */ if (option_mask32 & OPT_qq) { option_mask32 &= ~OPT_qq; alarm(50); } nfds--; recv_and_process_peer_pkt(idx2peer[j]); gettime1900d(); /* sets G.cur_time */ } } check_unsync: if (G.ntp_peers && G.stratum != MAXSTRAT) { for (item = G.ntp_peers; item != NULL; item = item->link) { peer_t *p = (peer_t *) item->data; if (p->reachable_bits) goto have_reachable_peer; } /* No peer responded for last 8 packets, panic */ clamp_pollexp_and_set_MAXSTRAT(); run_script("unsync", 0.0); have_reachable_peer: ; } } /* while (!bb_got_signal) */ remove_pidfile_std_path_and_ext("ntpd"); kill_myself_with_sig(bb_got_signal); }

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