我遇到了这段代码,想知道是否需要R / W Mutex。
method(){
var (
wg sync.WaitGroup
rwm sync.RWMutex
vcnRegionMap map[string][]core.Vcn
)
vcnRegionMap = make(map[string][]core.Vcn)
// This loops helps us in filtering unused regions
// for composition of region/vcnid ds
for _, regionName := range regions {
wg.Add(1)
go func(ctx context.Context, region string, vcnRegionMap map[string][]core.Vcn, wg *sync.WaitGroup, rwm *sync.RWMutex) {
// for locking maps
defer wg.Done()
// TODO: make this conditional if a region is specified
c.network.SetRegion(region)
vcnResponse, err := c.network.ListVcns(ctx, core.ListVcnsRequest{
CompartmentId: &c.cID,
})
if err != nil {
logger.Debug(err.Error())
}
if len(vcnResponse.Items) == 0 {
logger.Info("status 404: No Vcns found under the given OCID and region: %s", region)
return
}
logger.Info("status 200: Vcns found under the given OCID and region: %s", region)
for _, item := range vcnResponse.Items {
logger.Debug("Vcn object: %s", *item.DisplayName)
// maps are not concurrency safe
rwm.Lock()
defer rwm.Unlock()
vcnRegionMap[region] = append(vcnRegionMap[region], item)
}
}(ctx, regionName, vcnRegionMap, &wg, &rwm)
}
wg.Wait()
}
每个go例程获取其自己的map副本时,互斥量是否有帮助,我们是否可以避免它以减少延迟?
答案 0 :(得分:3)
您需要保护地图以防止同时访问。该代码是错误的,因为您正在读取互斥锁,但正在写入地图。
for _, item := range vcnResponse.Items {
logger.Debug("Vcn object: %s", *item.DisplayName)
// maps are not concurrency safe
rwm.Lock()
vcnRegionMap[region] = append(vcnRegionMap[region], item)
rwm.Unlock()
}
请注意,此版本不使用defer
。延迟操作在函数返回时运行,而不是在块结束时运行。您将互斥锁n
读锁定<?php
function csv(string $file, string $delimiter = ','): array{
$lines = file($file);
$lines[0] = str_replace("\xEF\xBB\xBF", '', $lines[0]);
$csv = array_map(function($d) use($delimiter) {
return str_getcsv($d, $delimiter);
}, $lines);
array_walk($csv, function(&$a) use ($csv) {
$a = array_combine($csv[0], $a);
});
array_shift($csv);
return $csv;
}
次,每次迭代一次,然后在函数返回时释放所有互斥量。