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Title: Waiting for goroutines to finish
URL slug: waitgroup
Description: A WaitGroup provides a simple way to wait for a collection of goroutines to perform a task.

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package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"log"
	"os"
)

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TL;DR: The proposal looks good, except the handler chaining part, which adds a lot of magical complexity to cater to rare use cases. Chaining can always be added at a later stage without breaking backwards compatibility, if its lack is deemed unbearable.

As I see it, the biggest issues in current Go usage the proposal tackles are:

1. Repeated sequences of if err != nil {return nil, err} littering Go code
2. Lack of proper context in propagated errors (see (1) above)

To fix these issues, I believe the proposed check keyword with a single handler per function are sufficient. Using stacks of handlers for proper cleanup is best left to defer, which is already a familiar tool. Thus, handle should only exist as a default "report more context in case of an error and return the error" mechanism. Where a single handler appears insufficient because the nature of error handling required changes throug

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from collections import namedtuple


TOK_TEXT        = 'TOK_TEXT'
TOK_LEFT_META   = 'TOK_LEFT_META'
TOK_RIGHT_META  = 'TOK_RIGHT_META'
TOK_DUMMY       = 'TOK_DUMMY'


# A token has

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const unsigned N = 400 * 1000 * 1000;

volatile unsigned long long counter = 0;

// Don't inline the benchmarking code into main
void __attribute__((noinline)) tightloop();
void __attribute__((noinline)) loop_with_extra_call();

void tightloop() {
  unsigned j;

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import io
from test.support import import_fresh_module

import csv

csv_other = import_fresh_module('csv', fresh=['_csv', 'csv'])

f = io.StringIO('foo\x00,bar\nbaz,42')
reader = csv.reader(f)

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====> lli
lli
  AsmParser
    Core
      Support
    Support
  BitReader
    Core
    Support
  IRReader

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struct SS {
  long n1;
  long n2;
  long n3;
  long n4;
};


int foo(struct SS s) {

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# Regex for matching/capturing role text.
# E.g. :name:`text` - first capture group is "name", second group is "text"
#
ROLE_REGEX = re.compile(r':(\w+):`([^`]*)`')

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class Timer(object):
    def __init__(self, name=None):
        self.name = name
    
    def __enter__(self):
        self.tstart = time.time()
        
    def __exit__(self, type, value, traceback):
        if self.name: