82 lines
1.7 KiB
Go
82 lines
1.7 KiB
Go
package runners
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import (
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"fmt"
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"sync"
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)
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// Processable defines a runnable process with error return
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// that can be passed to a Processor instance for managed running.
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type Processable func() error
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// Processor acts similarly to a sync.Once object, except that it is reusable. After
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// the first call to Process(), any further calls before this first has returned will
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// block until the first call has returned, and return the same error. This ensures
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// that only a single instance of it is ever running at any one time.
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type Processor struct {
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mutex sync.Mutex
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wait *sync.WaitGroup
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err *error
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}
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// Process will process the given function if first-call, else blocking until
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// the first function has returned, returning the same error result.
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func (p *Processor) Process(proc Processable) (err error) {
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// Acquire state lock.
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p.mutex.Lock()
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if p.wait != nil {
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// Already running.
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//
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// Get current ptrs.
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waitPtr := p.wait
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errPtr := p.err
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// Free state lock.
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p.mutex.Unlock()
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// Wait for finish.
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waitPtr.Wait()
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return *errPtr
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}
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// Alloc waiter for new process.
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var wait sync.WaitGroup
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// No need to alloc new error as
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// we use the alloc'd named error
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// return required for panic handling.
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// Reset ptrs.
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p.wait = &wait
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p.err = &err
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// Set started.
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wait.Add(1)
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p.mutex.Unlock()
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defer func() {
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if r := recover(); r != nil {
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if err != nil {
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rOld := r // wrap the panic so we don't lose existing returned error
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r = fmt.Errorf("panic occured after error %q: %v", err.Error(), rOld)
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}
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// Catch any panics and wrap as error.
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err = fmt.Errorf("caught panic: %v", r)
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}
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// Mark done.
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wait.Done()
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// Set stopped.
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p.mutex.Lock()
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p.wait = nil
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p.mutex.Unlock()
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}()
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// Run process.
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err = proc()
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return
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}
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