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Rewrite startup/shutdown logic to simplify shutdown signaling. All cleanup is now run from deferred functions in the main function. Add two new config options to set the read and write ends of a pair of pipes. This is used as a simple mechanism for a parent process to communicate with, observe, and manage the lifetime of a child dcrd process. When the RX (read end) pipe is closed, clean shutdown automatically begins. Add a new flag --lifetimeevents to create and send lifetime event notifications over the TX (write end) pipe during bringup and shutdown. This allows the parent process to observe which subsystems are currently starting, running, and stopping. Fixes #297. Fixes #298.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,207 @@ | ||
| // Copyright (c) 2016 The Decred developers | ||
| // Use of this source code is governed by an ISC | ||
| // license that can be found in the LICENSE file. | ||
|
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| package main | ||
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||
| import ( | ||
| "bufio" | ||
| "encoding/binary" | ||
| "fmt" | ||
| "io" | ||
| "os" | ||
| ) | ||
|
|
||
| // Messages sent over a pipe are encoded using a simple binary message format: | ||
| // | ||
| // - Message type length (1 byte) | ||
| // - Message type string (encoded as UTF8, no longer than 255 bytes) | ||
| // - Message payload length (4 bytes, little endian) | ||
| // - Message payload bytes (no longer than 2^32 - 1 bytes) | ||
| type pipeMessage interface { | ||
| Type() string | ||
| PayloadSize() uint32 | ||
| WritePayload(w io.Writer) error | ||
| } | ||
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| var outgoingPipeMessages = make(chan pipeMessage) | ||
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| // serviceControlPipeRx reads from the file descriptor fd of a read end pipe. | ||
| // This is intended to be used as a simple control mechanism for parent | ||
| // processes to communicate with and and manage the lifetime of a dcrd child | ||
| // process using a unidirectional pipe (on Windows, this is an anonymous pipe, | ||
| // not a named pipe). | ||
| // | ||
| // When the pipe is closed or any other errors occur reading the control | ||
| // message, shutdown begins. This prevents dcrd from continuing to run | ||
| // unsupervised after the parent process closes unexpectedly. | ||
| // | ||
| // No control messages are currently defined and the only use for the pipe is to | ||
| // start clean shutdown when the pipe is closed. Control messages that follow | ||
| // the pipe message format can be added later as needed. | ||
| func serviceControlPipeRx(fd uintptr) { | ||
| pipe := os.NewFile(fd, fmt.Sprintf("|%v", fd)) | ||
| r := bufio.NewReader(pipe) | ||
| for { | ||
| _, err := r.Discard(1024) | ||
| if err == io.EOF { | ||
| err = nil | ||
| break | ||
| } | ||
| if err != nil { | ||
| dcrdLog.Errorf("Failed to read from pipe: %v", err) | ||
| break | ||
| } | ||
| } | ||
|
|
||
| select { | ||
| case shutdownRequestChannel <- struct{}{}: | ||
| default: | ||
| } | ||
| } | ||
|
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| // serviceControlPipeTx sends pipe messages to the file descriptor fd of a write | ||
| // end pipe. This is intended to be a simple response and notification system | ||
| // for a child dcrd process to communicate with a parent process without the | ||
| // need to go through the RPC server. | ||
| // | ||
| // See the comment on the pipeMessage interface for the binary encoding of a | ||
| // pipe message. | ||
| func serviceControlPipeTx(fd uintptr) { | ||
| defer drainOutgoingPipeMessages() | ||
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| pipe := os.NewFile(fd, fmt.Sprintf("|%v", fd)) | ||
| w := bufio.NewWriter(pipe) | ||
| headerBuffer := make([]byte, 0, 1+255+4) // capped to max header size | ||
| var err error | ||
| for m := range outgoingPipeMessages { | ||
| mtype := m.Type() | ||
| psize := m.PayloadSize() | ||
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| headerBuffer = append(headerBuffer, byte(len(mtype))) | ||
| headerBuffer = append(headerBuffer, mtype...) | ||
| buf := make([]byte, 4) | ||
| binary.LittleEndian.PutUint32(buf, psize) | ||
| headerBuffer = append(headerBuffer, buf...) | ||
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| _, err = w.Write(headerBuffer) | ||
| if err != nil { | ||
| break | ||
| } | ||
|
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| err = m.WritePayload(w) | ||
| if err != nil { | ||
| break | ||
| } | ||
|
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| err = w.Flush() | ||
| if err != nil { | ||
| break | ||
| } | ||
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| headerBuffer = headerBuffer[:0] | ||
| } | ||
|
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| dcrdLog.Errorf("Failed to write to pipe: %v", err) | ||
| } | ||
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| func drainOutgoingPipeMessages() { | ||
| for range outgoingPipeMessages { | ||
| } | ||
| } | ||
|
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| // The lifetimeEvent describes a startup or shutdown event. The message type | ||
| // string is "lifetimeevent". | ||
| // | ||
| // The payload size is always 2 bytes long. The first byte describes whether a | ||
| // service or event is about to run or whether startup has completed. The | ||
| // second byte, when applicable, describes which event or service is about to | ||
| // start or stop. | ||
| // | ||
| // 0 <event id>: The startup event is about to run | ||
| // 1 <ignored>: All startup tasks have completed | ||
| // 2 <event id>: The shutdown event is about to run | ||
| // | ||
| // Event IDs can take on the following values: | ||
| // | ||
| // 0: Database opening/closing | ||
| // 1: Ticket database opening/closing | ||
| // 2: Peer-to-peer server starting/stopping | ||
| // | ||
| // Note that not all subsystems are started/stopped or events run during the | ||
| // program's lifetime depending on what features are enabled through the config. | ||
| // | ||
| // As an example, the following messages may be sent during a typical execution: | ||
| // | ||
| // 0 0: The database is being opened | ||
| // 0 1: The ticket DB is being opened | ||
| // 0 2: The P2P server is starting | ||
| // 1 0: All startup tasks have completed | ||
| // 2 2: The P2P server is stopping | ||
| // 2 1: The ticket DB is being closed and written to disk | ||
| // 2 0: The database is being closed | ||
| type lifetimeEvent struct { | ||
| event lifetimeEventID | ||
| action lifetimeAction | ||
| } | ||
|
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| var _ pipeMessage = (*lifetimeEvent)(nil) | ||
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| type lifetimeEventID byte | ||
|
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| const ( | ||
| startupEvent lifetimeEventID = iota | ||
| startupComplete | ||
| shutdownEvent | ||
| ) | ||
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| type lifetimeAction byte | ||
|
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| const ( | ||
| lifetimeEventDBOpen lifetimeAction = iota | ||
| lifetimeEventTicketDB | ||
| lifetimeEventP2PServer | ||
| ) | ||
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| func (*lifetimeEvent) Type() string { return "lifetimeevent" } | ||
| func (e *lifetimeEvent) PayloadSize() uint32 { return 2 } | ||
| func (e *lifetimeEvent) WritePayload(w io.Writer) error { | ||
| _, err := w.Write([]byte{byte(e.event), byte(e.action)}) | ||
| return err | ||
| } | ||
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| type lifetimeEventServer chan<- pipeMessage | ||
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| func newLifetimeEventServer(outChan chan<- pipeMessage) lifetimeEventServer { | ||
| return lifetimeEventServer(outChan) | ||
| } | ||
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| func (s lifetimeEventServer) notifyStartupEvent(action lifetimeAction) { | ||
| if s == nil { | ||
| return | ||
| } | ||
| s <- &lifetimeEvent{ | ||
| event: startupEvent, | ||
| action: action, | ||
| } | ||
| } | ||
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| func (s lifetimeEventServer) notifyStartupComplete() { | ||
| if s == nil { | ||
| return | ||
| } | ||
| s <- &lifetimeEvent{ | ||
| event: startupComplete, | ||
| action: 0, | ||
| } | ||
| } | ||
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| func (s lifetimeEventServer) notifyShutdownEvent(action lifetimeAction) { | ||
| if s == nil { | ||
| return | ||
| } | ||
| s <- &lifetimeEvent{ | ||
| event: shutdownEvent, | ||
| action: action, | ||
| } | ||
| } |
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