我该如何实现catch块中的代码？
try
{
// Call a MS SQL stored procedure (MS SQL 2000)
// Stored Procedure may deadlock
}
catch
{
// if deadlocked Call a MS SQL stored procedure (may deadlock again)
// If deadlocked, keep trying until stored procedure executes
}
finally
{
}
这样做并不被推荐，并且可能会在你的程序中引发严重问题。例如，如果数据库宕机了怎么办？
但是，以下是如何在循环中执行此操作的方法：
for(int attempts = 0; attempts < 5; attempts++)
// if you really want to keep going until it works, use for(;;)
{
try
{
DoWork();
break;
}
catch { }
Thread.Sleep(50); // Possibly a good idea to pause here, explanation below
}
Thread.Sleep 方法会暂停执行指定数量的毫秒。没有错误是完全随机的，大多数只需要再试一次就可以工作是因为在尝试之间所花费的时间内发生了某些变化。暂停线程的执行将为这种情况提供更大的机会窗口（例如，数据库引擎启动的时间更长）。bool retry = true;
while( retry ){
try{
...
retry = false;
}
catch
{
...
}
finally
{
...
}
}
以下内容摘自微软开发者网络页面，介绍了他们所谓的“重试模式”（Retry Pattern）：
private int retryCount = 3;
...
public async Task OperationWithBasicRetryAsync()
{
int currentRetry = 0;
for (; ;)
{
try
{
// Calling external service.
await TransientOperationAsync();
// Return or break.
break;
}
catch (Exception ex)
{
Trace.TraceError("Operation Exception");
currentRetry++;
// Check if the exception thrown was a transient exception
// based on the logic in the error detection strategy.
// Determine whether to retry the operation, as well as how
// long to wait, based on the retry strategy.
if (currentRetry > this.retryCount || !IsTransient(ex))
{
// If this is not a transient error
// or we should not retry re-throw the exception.
throw;
}
}
// Wait to retry the operation.
// Consider calculating an exponential delay here and
// using a strategy best suited for the operation and fault.
Await.Task.Delay();
}
}
// Async method that wraps a call to a remote service (details not shown).
private async Task TransientOperationAsync()
{
...
}
他们详细解释了此模式的适当使用和不适当使用。例如，如果您预计遇到的错误是短暂的，并且稍后重试可能会成功，那么这可能适合您。如果这是为了帮助您处理一些扩展问题，那么这并不适合您。
您还可能对他们的断路器模式感兴趣，他们将其描述为能够“处理连接到远程服务或资源时可能需要不同时间来纠正的故障。”
while (!success) {
try
{
// Call a MS SQL stored procedure (MS SQL 2000)
// Stored Procedure may deadlock
success = true;
}
catch
{
// if deadlocked Call a MS SQL stored procedure (may deadlock again)
// If deadlocked, keep trying until stored procedure executes
success = false;
}
}
Boolean succeeded = false;
while (!succeeded)
{
try
{
// Call a MS SQL stored procedure (MS SQL 2000)
// Stored Procedure may deadlock
succeeded = true;
}
catch (Exception ex)
{
// Log
}
}
类似于：
bool quit = false;
int loopcount = 0;
while(!quit )
{
try
{
// execute the command, might throw an exception)
quit = true; // no exception if you got here
}
catch(Exception ex)
{
if (ex != deadlock) // doesn't work like this :-(
quit = true;
}
finally
{
// etc.
}
loopcount++;
if (loopcount > 3)
quit = true;
}