frostfs-node/pkg/local_object_storage/writecache/mode.go

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package writecache
import (
"errors"
"time"
)
// Mode represents write-cache mode of operation.
type Mode uint32
const (
// ModeReadWrite is a default mode allowing objects to be flushed.
ModeReadWrite Mode = iota
// ModeReadOnly is a mode in which write-cache doesn't flush anything to a metabase.
ModeReadOnly
)
// ErrReadOnly is returned when Put/Write is performed in a read-only mode.
var ErrReadOnly = errors.New("write-cache is in read-only mode")
// SetMode sets write-cache mode of operation.
// When shard is put in read-only mode all objects in memory are flushed to disk
// and all background jobs are suspended.
func (c *cache) SetMode(m Mode) {
c.modeMtx.Lock()
defer c.modeMtx.Unlock()
if c.mode == m {
return
}
c.mode = m
if m == ModeReadWrite {
return
}
// Because modeMtx is taken no new objects will arrive an all other modifying
// operations are completed.
// 1. Persist objects already in memory on disk.
c.persistMemoryCache()
// 2. Suspend producers to ensure there are channel send operations in fly.
// metaCh and directCh can be populated either during Put or in background memory persist thread.
// Former possibility is eliminated by taking `modeMtx` mutex and
// latter by explicit persist in the previous step.
// flushCh is populated by `flush` with `modeMtx` is also taken.
// Thus all producers are shutdown and we only need to wait until all channels are empty.
for len(c.metaCh) != 0 || len(c.directCh) != 0 || len(c.flushCh) != 0 {
c.log.Info("waiting for channels to flush")
time.Sleep(time.Second)
}
}