README
¶
Overseer
Simple process manager library.
The useful methods are:
NewOverseer()- Returns a new instance of a process manager. To register processes, use theAdd(id string, args ...string)method, and to unregister use theRemove(id string)method.SuperviseAll()- This is the main function. Supervise all processes and block until they finish. This includes killing all the processes when the main program exits.Supervise(id string)- Supervise one registered process and block until it finishes. This includes checking if the process was killed from the outside, delaying the start and restarting in case of failure.Stop(id string)- Stops the process by sending its process group a SIGTERM signal.Signal(id string, sig syscall.Signal)- Signal sends an OS signal to the process group.StopAll()- Cycles and stops all processes by sending SIGTERM.
For more examples of usage, please check the tests, for now.
Similar libraries
- https://github.com/go-cmd/cmd - os/exec.Cmd with concurrent-safe access, real-time streaming output and complete runtime/return status. Overseer is based off this one.
- https://github.com/immortal/immortal - A *nix cross-platform (OS agnostic) supervisor. The real deal.
- https://github.com/ochinchina/supervisord - A Golang supervisor implementation, inspired by Python supervisord.
Icon is made by Freepik from www.flaticon.com and licensed by CC 3.0 BY.
License
MIT © Cristi Constantin.
Documentation
¶
Overview ¶
Package cmd runs external commands with concurrent access to output and status. It wraps the Go standard library os/exec.Command to correctly handle reading output (STDOUT and STDERR) while a command is running and killing a command. All operations are safe to call from multiple goroutines.
Credit: https://github.com/go-cmd/cmd Copyright (c) 2017 go-cmd & contribuitors The architecture is quite heavily modified from the original version
A basic example that runs env and prints its output:
import (
"fmt"
"github.com/go-cmd/cmd"
)
func main() {
// Create Cmd, buffered output
envCmd := cmd.NewCmd("env")
// Run and wait for Cmd to return Status
status := <-envCmd.Start()
// Print each line of STDOUT from Cmd
for _, line := range status.Stdout {
fmt.Println(line)
}
}
Commands can be ran synchronously (blocking) or asynchronously (non-blocking):
envCmd := cmd.NewCmd("env") // create
status := <-envCmd.Start() // run blocking
statusChan := envCmd.Start() // run non-blocking
// Do other work while Cmd is running...
status <- statusChan // blocking
Start returns a channel to which the final Status is sent when the command finishes for any reason. The first example blocks receiving on the channel. The second example is non-blocking because it saves the channel and receives on it later. Only one final status is sent to the channel; use Done for multiple goroutines to wait for the command to finish, then call Status to get the final status.
Index ¶
- Constants
- type Backoff
- type Cmd
- func (c *Cmd) CloneCmd() *Cmd
- func (c *Cmd) Done() <-chan struct{}
- func (c *Cmd) IsFinalState() bool
- func (c *Cmd) SetDelayStart(delayStart uint)
- func (c *Cmd) SetDir(dir string)
- func (c *Cmd) SetEnv(env []string)
- func (c *Cmd) SetRetryTimes(retryTimes uint)
- func (c *Cmd) Signal(sig syscall.Signal) error
- func (c *Cmd) Start() <-chan Status
- func (c *Cmd) Status() Status
- func (c *Cmd) Stop() error
- func (c *Cmd) ToJSON() JSONProcess
- type CmdState
- type ErrLineBufferOverflow
- type JSONProcess
- type Options
- type OutputBuffer
- type OutputStream
- type Overseer
- func (ovr *Overseer) Add(id string, args ...string) *Cmd
- func (ovr *Overseer) HasProc(id string) bool
- func (ovr *Overseer) ListAll() []string
- func (ovr *Overseer) Remove(id string) bool
- func (ovr *Overseer) Signal(id string, sig syscall.Signal) error
- func (ovr *Overseer) Status(id string) Status
- func (ovr *Overseer) Stop(id string) error
- func (ovr *Overseer) StopAll()
- func (ovr *Overseer) Supervise(id string)
- func (ovr *Overseer) SuperviseAll()
- func (ovr *Overseer) ToJSON(id string) JSONProcess
- type Status
Constants ¶
const ( // DEFAULT_LINE_BUFFER_SIZE is the default size of the OutputStream line buffer. // The default value is usually sufficient, but if ErrLineBufferOverflow errors // occur, try increasing the size by calling OutputBuffer.SetLineBufferSize. DEFAULT_LINE_BUFFER_SIZE = 16384 // DEFAULT_STREAM_CHAN_SIZE is the default string channel size for a Cmd when // Options.Streaming is true. The string channel size can have a minor // performance impact if too small by causing OutputStream.Write to block // excessively. DEFAULT_STREAM_CHAN_SIZE = 1000 )
const ( INITIAL CmdState = iota STARTING = 10 RUNNING = 20 STOPPING = 30 INTERRUPT = 40 // final state (used when stopped or signaled) FINISHED = 50 // final state (used then was a natural exit) FATAL = 60 // final state (used when was an error while starting) UNKNOWN = 99 )
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type Backoff ¶
type Backoff struct {
//Factor is the multiplying factor for each increment step
Factor float64
//Jitter eases contention by randomizing backoff steps
Jitter bool
//Min and Max are the minimum and maximum values of the counter
Min, Max time.Duration
// contains filtered or unexported fields
}
Backoff is a time.Duration counter, starting at Min. After every call to the Duration method the current timing is multiplied by Factor, but it never exceeds Max.
Backoff is not generally concurrent-safe, but the ForAttempt method can be used concurrently.
func (*Backoff) Duration ¶
Duration returns the duration for the current attempt before incrementing the attempt counter. See ForAttempt.
func (*Backoff) ForAttempt ¶
ForAttempt returns the duration for a specific attempt. This is useful if you have a large number of independent Backoffs, but don't want use unnecessary memory storing the Backoff parameters per Backoff. The first attempt should be 0.
ForAttempt is concurrent-safe.
type Cmd ¶
type Cmd struct {
Name string
Args []string
Env []string
Dir string
DelayStart uint // Nr of milli-seconds to delay the start (used by the manager)
RetryTimes uint // Nr of times to restart on failure (used by the manager)
Stdout chan string // streaming STDOUT if enabled, else nil (see Options)
Stderr chan string // streaming STDERR if enabled, else nil (see Options)
State CmdState // The state of the cmd (stopped, started, etc)
*sync.Mutex
// contains filtered or unexported fields
}
Cmd represents an external command, similar to the Go built-in os/exec.Cmd. A Cmd cannot be reused after calling Start. Exported fields are read-only and should not be modified, except Env which can be set before calling Start. To create a new Cmd, call NewCmd or NewCmdOptions.
func NewCmd ¶
NewCmd creates a new Cmd for the given command name and arguments. The command is not started until Start is called. Output buffering is on, streaming output is off. To control output, use NewCmdOptions instead.
func NewCmdOptions ¶
NewCmdOptions creates a new Cmd with options. The command is not started until Start is called.
func (*Cmd) CloneCmd ¶
CloneCmd clones a Cmd. All the configs are transferred, and the state of the original object is lost.
func (*Cmd) Done ¶
func (c *Cmd) Done() <-chan struct{}
Done returns a channel that's closed when the command stops running. This method is useful for multiple goroutines to wait for the command to finish.Call Status after the command finishes to get its final status.
func (*Cmd) IsFinalState ¶
IsFinalState returns true if the Cmd is in a final state. Final states are definitive and cannot be exited from.
func (*Cmd) SetDelayStart ¶
SetDelayStart sets the delay start in milli-seconds.
func (*Cmd) SetDir ¶
SetDir sets the environment variables for the launched command. This can only have effect before starting the command.
func (*Cmd) SetEnv ¶
SetEnv sets the working directory of the command. This can only have effect before starting the command.
func (*Cmd) SetRetryTimes ¶
SetRetryTimes sets the times of restart in case of failure.
func (*Cmd) Start ¶
Start starts the command and immediately returns a channel that the caller can use to receive the final Status of the command when it ends. The caller can start the command and wait like,
status := <-myCmd.Start() // blocking
or start the command asynchronously and be notified later when it ends,
statusChan := myCmd.Start() // non-blocking // Do other work while Cmd is running... status := <-statusChan // blocking
Exactly one Status is sent on the channel when the command ends. The channel is not closed. Any Go error is set to Status.Error. Start is idempotent; it always returns the same channel.
func (*Cmd) Status ¶
Status returns the Status of the command at any time. It is safe to call concurrently by multiple goroutines.
With buffered output, Status.Stdout and Status.Stderr contain the full output as of the Status call time. For example, if the command counts to 3 and three calls are made between counts, Status.Stdout contains:
"1" "1 2" "1 2 3"
The caller is responsible for tailing the buffered output if needed. Else, consider using streaming output. When the command finishes, buffered output is complete and final.
Status.Runtime is updated while the command is running and final when it finishes.
func (*Cmd) Stop ¶
Stop stops the command by sending its process group a SIGTERM signal. Stop is idempotent. An error should only be returned in the rare case that Stop is called immediately after the command ends but before Start can update its internal state.
func (*Cmd) ToJSON ¶
func (c *Cmd) ToJSON() JSONProcess
ToJSON returns JSON friendly detailed info about the Cmd.
type ErrLineBufferOverflow ¶
type ErrLineBufferOverflow struct {
Line string // Unterminated line that caused the error
BufferSize int // Internal line buffer size
BufferFree int // Free bytes in line buffer
}
ErrLineBufferOverflow is returned by OutputStream.Write when the internal line buffer is filled before a newline character is written to terminate a line. Increasing the line buffer size by calling OutputStream.SetLineBufferSize can help prevent this error.
func (ErrLineBufferOverflow) Error ¶
func (e ErrLineBufferOverflow) Error() string
type JSONProcess ¶
type JSONProcess struct {
Cmd string `json:"cmd"`
PID int `json:"PID"`
State string `json:"state"`
ExitCode int `json:"exitCode"` // exit code of process
Error error `json:"error"` // Go error
RunTime float64 `json:"runTime"` // seconds, zero if Cmd not started
StartTime time.Time `json:"startTime"`
Dir string `json:"dir"`
DelayStart uint `json:"delayStart"`
RetryTimes uint `json:"retryTimes"`
}
JSONProcess structure
type Options ¶
type Options struct {
// If Buffered is true, STDOUT and STDERR are written to Status.Stdout and
// Status.Stderr. The caller can call Cmd.Status to read output at intervals.
// See Cmd.Status for more info.
Buffered bool
// If Streaming is true, Cmd.Stdout and Cmd.Stderr channels are created and
// STDOUT and STDERR output lines are written them in real time. This is
// faster and more efficient than polling Cmd.Status. The caller must read both
// streaming channels, else lines are dropped silently.
Streaming bool
}
Options represents customizations for NewCmdOptions.
type OutputBuffer ¶
OutputBuffer represents command output that is saved, line by line, in an unbounded buffer. It is safe for multiple goroutines to read while the command is running and after it has finished. If output is small (a few megabytes) and not read frequently, an output buffer is a good solution.
A Cmd in this package uses an OutputBuffer for both STDOUT and STDERR by default when created by calling NewCmd. To use OutputBuffer directly with a Go standard library os/exec.Command:
import "os/exec" import "github.com/go-cmd/cmd" runnableCmd := exec.Command(...) stdout := cmd.NewOutputBuffer() runnableCmd.Stdout = stdout
While runnableCmd is running, call stdout.Lines() to read all output currently written.
func NewOutputBuffer ¶
func NewOutputBuffer() *OutputBuffer
NewOutputBuffer creates a new output buffer. The buffer is unbounded and safe for multiple goroutines to read while the command is running by calling Lines.
func (*OutputBuffer) Lines ¶
func (rw *OutputBuffer) Lines() []string
Lines returns lines of output written by the Cmd. It is safe to call while the Cmd is running and after it has finished. Subsequent calls returns more lines, if more lines were written. "\r\n" are stripped from the lines.
type OutputStream ¶
type OutputStream struct {
// contains filtered or unexported fields
}
OutputStream represents real time, line by line output from a running Cmd. Lines are terminated by a single newline preceded by an optional carriage return. Both newline and carriage return are stripped from the line when sent to a caller-provided channel.
The caller must begin receiving before starting the Cmd. Write blocks on the channel; the caller must always read the channel. The channel is not closed by the OutputStream.
A Cmd in this package uses an OutputStream for both STDOUT and STDERR when created by calling NewCmdOptions and Options.Streaming is true. To use OutputStream directly with a Go standard library os/exec.Command:
import "os/exec"
import "github.com/go-cmd/cmd"
stdoutChan := make(chan string, 100)
go func() {
for line := range stdoutChan {
// Do something with the line
}
}()
runnableCmd := exec.Command(...)
stdout := cmd.NewOutputStream(stdoutChan)
runnableCmd.Stdout = stdout
While runnableCmd is running, lines are sent to the channel as soon as they are written and newline-terminated by the command. After the command finishes, the caller should wait for the last lines to be sent:
for len(stdoutChan) > 0 {
time.Sleep(10 * time.Millisecond)
}
Since the channel is not closed by the OutputStream, the two indications that all lines have been sent and received are the command finishing and the channel size being zero.
func NewOutputStream ¶
func NewOutputStream(streamChan chan string) *OutputStream
NewOutputStream creates a new streaming output on the given channel. The caller must begin receiving on the channel before the command is started. The OutputStream never closes the channel.
func (*OutputStream) Lines ¶
func (rw *OutputStream) Lines() <-chan string
Lines returns the channel to which lines are sent. This is the same channel passed to NewOutputStream.
func (*OutputStream) SetLineBufferSize ¶
func (rw *OutputStream) SetLineBufferSize(n int)
SetLineBufferSize sets the internal line buffer size. The default is DEFAULT_LINE_BUFFER_SIZE. This function must be called immediately after NewOutputStream, and it is not safe to call by multiple goroutines.
Increasing the line buffer size can help reduce ErrLineBufferOverflow errors.
type Overseer ¶
type Overseer struct {
// contains filtered or unexported fields
}
Overseer structure. For instantiating, it's best to use the NewOverseer() function.
func NewOverseer ¶
func NewOverseer() *Overseer
NewOverseer creates a new Overseer. After creating it, add the procs and call SuperviseAll.
func (*Overseer) Status ¶
Status returns a child process status (PID, Exit code, Error, Runtime seconds, Stdout, Stderr)
func (*Overseer) Stop ¶
Stop the process by sending its process group a SIGTERM signal. The process can be started again, if needed.
func (*Overseer) StopAll ¶
func (ovr *Overseer) StopAll()
StopAll cycles and kills all child procs. Used when exiting the program.
func (*Overseer) SuperviseAll ¶
func (ovr *Overseer) SuperviseAll()
SuperviseAll is the *main* function. Supervise all registered processes and wait for them to finish.
func (*Overseer) ToJSON ¶
func (ovr *Overseer) ToJSON(id string) JSONProcess
ToJSON returns a more detailed process status, ready to be converted to JSON.
type Status ¶
type Status struct {
Cmd string
PID int
Exit int // exit code of process
Error error // Go error
StartTs int64 // Unix ts (nanoseconds), zero if Cmd not started
StopTs int64 // Unix ts (nanoseconds), zero if Cmd not started or running
Runtime float64 // seconds, zero if Cmd not started
Stdout []string // buffered STDOUT; see Cmd.Status for more info
Stderr []string // buffered STDERR; see Cmd.Status for more info
}
Status represents the running status and consolidated return of a Cmd. It can be obtained any time by calling Cmd.Status. If StartTs > 0, the command has started. If StopTs > 0, the command has stopped. After the command finishes for any reason, this combination of values indicates success (presuming the command only exits zero on success):
Exit = 0 Error = nil
Error is a Go error from the underlying os/exec.Cmd.Start or os/exec.Cmd.Wait. If not nil, the command either failed to start (it never ran) or it started but was terminated unexpectedly (probably signaled). In either case, the command failed. Callers should check Error first. If nil, then check Exit and Status.
Source Files