source: benchmark/readyQ/locality.go@ 751e2eb

package main

import (
        "context"
        "flag"
        "fmt"
        "math/rand"
        "os"
        "syscall"
        "sync/atomic"
        "time"
        "unsafe"
        "golang.org/x/sync/semaphore"
        "golang.org/x/text/language"
        "golang.org/x/text/message"
)

// ==================================================
type MyData struct {
        ttid int
        id int
        data [] uint64
}

func NewData(id int, size uint64) (*MyData) {
        var data [] uint64
        data = make([]uint64, size)
        for i := uint64(0); i < size; i++ {
                data[i] = 0
        }
        return &MyData{syscall.Gettid(), id, data}
}

func (this * MyData) moved( ttid int ) (uint64) {
        if this.ttid == ttid {
                return 0
        }
        this.ttid = ttid
        return 1
}

func (this * MyData) access( idx uint64 ) {
        this.data[idx % uint64(len(this.data))] += 1
}

// ==================================================
type MyCtx struct {
        s * semaphore.Weighted
        d unsafe.Pointer
        c context.Context
        ttid int
        id int
}

func NewCtx( data * MyData, id int ) (MyCtx) {
        r := MyCtx{semaphore.NewWeighted(1), unsafe.Pointer(data), context.Background(), syscall.Gettid(), id}
        r.s.Acquire(context.Background(), 1)
        return r
}

func (this * MyCtx) moved( ttid int ) (uint64) {
        if this.ttid == ttid {
                return 0
        }
        this.ttid = ttid
        return 1
}

// ==================================================
// Atomic object where a single thread can wait
// May exchanges data
type Spot struct {
        ptr uintptr // atomic variable use fo MES
        id int      // id for debugging
}

// Main handshake of the code
// Single seat, first thread arriving waits
// Next threads unblocks current one and blocks in its place
// if share == true, exchange data in the process
func (this * Spot) put( ctx * MyCtx, data * MyData, share bool) (* MyData, bool) {
        new := uintptr(unsafe.Pointer(ctx))
        // old_d := ctx.d

        // Attempt to CAS our context into the seat
        var raw uintptr
        for true {
                raw = this.ptr
                if raw == uintptr(1) { // Seat is closed, return
                        return nil, true
                }
                if atomic.CompareAndSwapUintptr(&this.ptr, raw, new) {
                        break // We got the seat
                }
        }

        // If we aren't the fist in, wake someone
        if raw != uintptr(0) {
                var val *MyCtx
                val = (*MyCtx)(unsafe.Pointer(raw))

                // If we are sharing, give them our data
                if share {
                        // fmt.Printf("[%d] - %d update %d: %p -> %p\n", this.id, ctx.id, val.id, val.d, data)
                        atomic.StorePointer(&val.d, unsafe.Pointer(data))
                }

                // Wake them up
                // fmt.Printf("[%d] - %d release %d\n", this.id, ctx.id, val.id)
                val.s.Release(1)
        }

        // fmt.Printf("[%d] - %d enter\n", this.id, ctx.id)

        // Block once on the seat
        ctx.s.Acquire(ctx.c, 1)

        // Someone woke us up, get the new data
        ret := (* MyData)(atomic.LoadPointer(&ctx.d))
        // fmt.Printf("[%d] - %d leave: %p -> %p\n", this.id, ctx.id, ret, old_d)

        return ret, false
}

// Shutdown the spot
// Wake current thread and mark seat as closed
func (this * Spot) release() {
        val := (*MyCtx)(unsafe.Pointer(atomic.SwapUintptr(&this.ptr, uintptr(1))))
        if val == nil {
                return
        }

        // Someone was there, release them
        val.s.Release(1)
}

// ==================================================
// Struct for result, Go doesn't support passing tuple in channels
type Result struct {
        count uint64
        gmigs uint64
        dmigs uint64
}

func NewResult() (Result) {
        return Result{0, 0, 0}
}

// ==================================================
// Random number generator, Go's native one is to slow and global
func __xorshift64( state * uint64 ) (uint64) {
        x := *state
        x ^= x << 13
        x ^= x >> 7
        x ^= x << 17
        *state = x
        return x
}

// ==================================================
// Do some work by accessing 'cnt' cells in the array
func work(data * MyData, cnt uint64, state * uint64) {
        for i := uint64(0); i < cnt; i++ {
                data.access(__xorshift64(state))
        }
}

// Main body of the threads
func local(result chan Result, start chan struct{}, size uint64, cnt uint64, channels [] Spot, share bool, id int) {
        // Initialize some data
        state := rand.Uint64()    // RNG state
        data := NewData(id, size) // Starting piece of data
        ctx := NewCtx(data, id)   // Goroutine local context

        // Prepare results
        r := NewResult()

        // Wait for start
        <- start

        // Main loop
        for true {
                // Touch our current data, write to invalidate remote cache lines
                work(data, cnt, &state)

                // Wait on a random spot
                i := __xorshift64(&state) % uint64(len(channels))
                var closed bool
                data, closed = channels[i].put(&ctx, data, share)

                // Check if the experiment is over
                if closed { break }                                       // yes, spot was closed
                if  clock_mode && atomic.LoadInt32(&stop) == 1 { break }  // yes, time's up
                if !clock_mode && r.count >= stop_count { break }         // yes, iterations reached

                // Check everything is consistent
                if uint64(len(data.data)) != size { panic("Data has weird size") }

                // write down progress and check migrations
                ttid := syscall.Gettid()
                r.count += 1
                r.gmigs += ctx .moved(ttid)
                r.dmigs += data.moved(ttid)
        }

        // Mark goroutine as done
        atomic.AddInt64(&threads_left, -1);

        // return result
        result <- r
}

// ==================================================
// Program main
func main() {
        // Benchmark specific command line arguments
        work_sizeOpt := flag.Uint64("w", 2    , "Size of the array for each threads, in words (64bit)")
        countOpt     := flag.Uint64("c", 2    , "Number of words to touch when working (random pick, cells can be picked more than once)")
        shareOpt     := flag.Bool  ("s", false, "Pass the work data to the next thread when blocking")

        // General benchmark initialization and deinitialization
        defer bench_init()()

        // Eval command line arguments
        size  := *work_sizeOpt
        cnt   := *countOpt
        share := *shareOpt

        // Check params
        if ! (nthreads > nprocs) {
                fmt.Fprintf(os.Stderr, "Must have more threads than procs\n")
                os.Exit(1)
        }

        // Make global data
        barrierStart := make(chan struct{})         // Barrier used at the start
        threads_left = int64(nprocs)                // Counter for active threads (not 'nthreads' because at all times 'nthreads - nprocs' are blocked)
        result  := make(chan Result)                // Channel for results
        channels := make([]Spot, nthreads - nprocs) // Number of spots
        for i := range channels {
                channels[i] = Spot{uintptr(0), i}     // init spots
        }

        // start the goroutines
        for i := 0; i < nthreads; i++ {
                go local(result, barrierStart, size, cnt, channels, share, i)
        }
        fmt.Printf("Starting\n");

        atomic.StoreInt32(&stop, 0)
        start := time.Now()
        close(barrierStart) // release barrier

        wait(start, true);  // general benchmark wait

        atomic.StoreInt32(&stop, 1)
        end := time.Now()
        delta := end.Sub(start)

        fmt.Printf("\nDone\n")

        // release all the blocked threads
        for i := range channels {
                channels[i].release()
        }

        // Join and accumulate results
        results := NewResult()
        for i := 0; i < nthreads; i++ {
                r := <- result
                results.count += r.count
                results.gmigs += r.gmigs
                results.dmigs += r.dmigs
        }

        // Print with nice 's, i.e. 1'000'000 instead of 1000000
        p := message.NewPrinter(language.English)
        p.Printf("Duration (ms)          : %f\n", delta.Seconds());
        p.Printf("Number of processors   : %d\n", nprocs);
        p.Printf("Number of threads      : %d\n", nthreads);
        p.Printf("Work size (64bit words): %d\n", size);
        p.Printf("Total Operations(ops)  : %15d\n", results.count)
        p.Printf("Total G Migrations     : %15d\n", results.gmigs)
        p.Printf("Total D Migrations     : %15d\n", results.dmigs)
        p.Printf("Ops per second         : %18.2f\n", float64(results.count) / delta.Seconds())
        p.Printf("ns per ops             : %18.2f\n", float64(delta.Nanoseconds()) / float64(results.count))
        p.Printf("Ops per threads        : %15d\n", results.count / uint64(nthreads))
        p.Printf("Ops per procs          : %15d\n", results.count / uint64(nprocs))
        p.Printf("Ops/sec/procs          : %18.2f\n", (float64(results.count) / float64(nprocs)) / delta.Seconds())
        p.Printf("ns per ops/procs       : %18.2f\n", float64(delta.Nanoseconds()) / (float64(results.count) / float64(nprocs)))
}