57 lines
1.9 KiB
Go
57 lines
1.9 KiB
Go
package influxdb
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import (
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"context"
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"errors"
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"time"
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)
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// ErrNoAcquire is returned when it was not possible to acquire ownership of the
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// semaphore.
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var ErrNoAcquire = errors.New("ownership not acquired")
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// DefaultLeaseTTL is used when a specific lease TTL is not requested.
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const DefaultLeaseTTL = time.Minute
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// A Semaphore provides an API for requesting ownership of an expirable semaphore.
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//
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// Acquired semaphores have an expiration. If they're not released or kept alive
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// during this period then they will expire and ownership of the semaphore will
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// be lost.
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//
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// TODO(edd): add AcquireTTL when needed. It should block.
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type Semaphore interface {
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// TryAcquire attempts to acquire ownership of the semaphore. TryAcquire
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// must not block. Failure to get ownership of the semaphore should be
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// signalled to the caller via the return of the ErrNoAcquire error.
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TryAcquire(ctx context.Context, ttl time.Duration) (Lease, error)
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}
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// A Lease represents ownership over a semaphore. It gives the owner the ability
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// to extend ownership over the semaphore or release ownership of the semaphore.
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type Lease interface {
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// TTL returns the duration of time remaining before the lease expires.
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TTL(context.Context) (time.Duration, error)
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// Release terminates ownership of the semaphore by revoking the lease.
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Release(context.Context) error
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// KeepAlive extends the lease back to the original TTL.
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KeepAlive(context.Context) error
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}
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// NopSemaphore is a Semaphore that always hands out leases.
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var NopSemaphore Semaphore = nopSemaphore{}
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type nopSemaphore struct{}
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func (nopSemaphore) TryAcquire(ctx context.Context, ttl time.Duration) (Lease, error) {
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return nopLease{}, nil
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}
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type nopLease struct{}
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func (nopLease) TTL(context.Context) (time.Duration, error) { return DefaultLeaseTTL, nil }
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func (nopLease) Release(context.Context) error { return nil }
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func (nopLease) KeepAlive(context.Context) error { return nil }
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