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