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DistributedLockTaskDistributedLockTask
using System;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Npgsql;
namespace PostgreSQLDistributedLock
{
public sealed class DistributedLock : IDisposable
{
private readonly ILogger<DistributedLock> _logger;
private bool _disposed;
private NpgsqlConnection _connection;
public DistributedLock(string connectionString, ILogger<DistributedLock> logger)
{
_logger = logger;
var builder = new NpgsqlConnectionStringBuilder(connectionString);
_connection = new NpgsqlConnection(builder.ToString());
_connection.Open();
}
public async Task<bool> TryExecuteInDistributedLock(long lockId, Func<Task> exclusiveLockTask)
{
var hasLockedAcquired = await TryAcquireLockAsync(lockId);
if (!hasLockedAcquired)
{
return false;
}
try
{
await exclusiveLockTask();
}
finally
{
await ReleaseLock(lockId);
}
return true;
}
private async Task<bool> TryAcquireLockAsync(long lockId)
{
var sessionLockCommand = $"SELECT pg_try_advisory_lock({lockId})";
_logger.LogInformation("Trying to acquire session lock for Lock Id {@LockId}", lockId);
var commandQuery = new NpgsqlCommand(sessionLockCommand, _connection);
var result = await commandQuery.ExecuteScalarAsync();
if (result != null && bool.TryParse(result.ToString(), out var lockAcquired) && lockAcquired)
{
_logger.LogInformation("Lock {@LockId} acquired", lockId);
return true;
}
_logger.LogInformation("Lock {@LockId} rejected", lockId);
return false;
}
private async Task ReleaseLock(long lockId)
{
var transactionLockCommand = $"SELECT pg_advisory_unlock({lockId})";
_logger.LogInformation("Releasing session lock for {@LockId}", lockId);
var commandQuery = new NpgsqlCommand(transactionLockCommand, _connection);
await commandQuery.ExecuteScalarAsync();
}
public void Dispose()
{
Dispose(true);
}
private void Dispose(bool disposing)
{
if (_disposed)
{
return;
}
if (disposing)
{
_connection?.Close();
_connection?.Dispose();
_connection = null;
}
_disposed = true;
}
}
}
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