最大例行程序数

如果goroutine被阻止，则除以下内容外不涉及其他任何费用：

• 内存使用情况
• 较慢的垃圾收集

成本（就内存和实际开始执行goroutine的平均时间而言）为：

Go 1.6.2 (April 2016)  32-bit x86 CPU (A10-7850K 4GHz)    | Number of goroutines: 100000    | Per goroutine:    |   Memory: 4536.84 bytes    |   Time:   1.634248 µs  64-bit x86 CPU (A10-7850K 4GHz)    | Number of goroutines: 100000    | Per goroutine:    |   Memory: 4707.92 bytes    |   Time:   1.842097 µsGo release.r60.3 (December 2011)  32-bit x86 CPU (1.6 GHz)    | Number of goroutines: 100000    | Per goroutine:    |   Memory: 4243.45 bytes    |   Time:   5.815950 µs

在装有4 GB内存的计算机上，这会将goroutine的最大数量限制为略少于一百万。

源代码（如果您已经理解上面打印的数字，则无需阅读此书）：

package mainimport (    "flag"    "fmt"    "os"    "runtime"    "time")var n = flag.Int("n", 1e5, "Number of goroutines to create")var ch = make(chan byte)var counter = 0func f() {    counter++    <-ch // Block this goroutine}func main() {    flag.Parse()    if *n <= 0 { fmt.Fprintf(os.Stderr, "invalid number of goroutines") os.Exit(1)    }    // Limit the number of spare OS threads to just 1    runtime.GOMAXPROCS(1)    // Make a copy of MemStats    var m0 runtime.MemStats    runtime.ReadMemStats(&m0)    t0 := time.Now().UnixNano()    for i := 0; i < *n; i++ { go f()    }    runtime.Gosched()    t1 := time.Now().UnixNano()    runtime.GC()    // Make a copy of MemStats    var m1 runtime.MemStats    runtime.ReadMemStats(&m1)    if counter != *n { fmt.Fprintf(os.Stderr, "failed to begin execution of all goroutines") os.Exit(1)    }    fmt.Printf("Number of goroutines: %dn", *n)    fmt.Printf("Per goroutine:n")    fmt.Printf("  Memory: %.2f bytesn", float64(m1.Sys-m0.Sys)/float64(*n))    fmt.Printf("  Time:   %f µsn", float64(t1-t0)/float64(*n)/1e3)}