[英]Using lock statement in c#
I need to use the lock construction, and edit the following methods to execute in parallel:我需要使用锁结构,并编辑以下方法以并行执行:
public void Withdraw(int amountToWithdraw)
{
if (amountToWithdraw <= 0)
{
throw new ArgumentException("The amount should be greater than 0.");
}
if (amountToWithdraw > MaxAmountPerTransaction)
{
throw new ArgumentException($"The value {amountToWithdraw} exceeds transaction limit: {MaxAmountPerTransaction}.");
}
if (amountToWithdraw > Amount)
{
throw new ArgumentException("Insufficient funds.");
}
WithdrawAndEmulateTransactionDelay(amountToWithdraw);
}
Here is the result这是结果
private readonly object balanceLock = new object();
public void Withdraw(int amountToWithdraw)
{
if (amountToWithdraw <= 0)
{
throw new ArgumentException("The amount should be greater than 0.");
}
if (amountToWithdraw > MaxAmountPerTransaction)
{
throw new ArgumentException($"The value {amountToWithdraw} exceeds transaction limit: {MaxAmountPerTransaction}.");
}
if (amountToWithdraw > Amount)
{
throw new ArgumentException("Insufficient funds.");
}
lock (balanceLock)
{
WithdrawAndEmulateTransactionDelay(amountToWithdraw);
}
}
This is a description of the method WithdrawAndEmulateTransactionDelay which shouldn't be changed这是对不应更改的方法 WithdrawAndEmulateTransactionDelay 的描述
private void WithdrawAndEmulateTransactionDelay(int amountToWithdraw)
{
Thread.Sleep(1000);
Amount -= amountToWithdraw;
}
However, the unit test failed.但是,单元测试失败了。 Where is the mistake in my code?我的代码中的错误在哪里?
It seems, that you should put the last validation within the lock: in your current implementation it's possible that看来,您应该将最后一个验证放在锁中:在您当前的实现中,有可能
cash1
, which is valid ( cash1 < Account
), validation's passed线程 #1 尝试提取有效的cash1
( cash1 < Account
),验证通过cash2
, which is valid ( cash2 < Account
), validation's passed线程 #2 尝试提取有效的cash2
( cash2 < Account
),验证通过cash1 + cash2 > Account
但是cash1 + cash2 > Account
WithdrawAndEmulateTransactionDelay
, now Amount == Amount - cash1 < cash2
线程 #1 调用WithdrawAndEmulateTransactionDelay
,现在Amount == Amount - cash1 < cash2
WithdrawAndEmulateTransactionDelay
;线程#2 调用WithdrawAndEmulateTransactionDelay
; since Amount - cash1 < cash2
you have the test failed因为Amount - cash1 < cash2
你有测试失败private readonly object balanceLock = new object();
public void Withdraw(int amountToWithdraw) {
// These validations are not depended on Amount, they don't want lock
if (amountToWithdraw <= 0)
throw new ArgumentOutOfRangeException(nameof(amountToWithdraw),
"The amount should be greater than 0.");
if (amountToWithdraw > MaxAmountPerTransaction)
throw new ArgumentOutOfRangeException(nameof(amountToWithdraw),
$"The value {amountToWithdraw} exceeds transaction limit: {MaxAmountPerTransaction}.");
// from now on we start using Amount, so we need the lock:
lock (balanceLock) {
if (amountToWithdraw > Amount)
throw new ArgumentException("Insufficient funds.", nameof(amountToWithdraw));
WithdrawAndEmulateTransactionDelay(amountToWithdraw);
}
}
I'd also avoid all of those exceptions.我也会避免所有这些例外。 Bad input is this code is often to be expected so it's not exceptional.错误的输入是这个代码通常是意料之中的,所以它并不例外。
Try this code:试试这个代码:
public TransactionStatus Withdraw(int amountToWithdraw)
{
bool successful = false;
string message = "OK";
int balanceBefore = Amount;
int balanceAfter = Amount;
if (amountToWithdraw <= 0)
{
message = "The amount should be greater than 0.";
}
else if (amountToWithdraw > MaxAmountPerTransaction)
{
message = $"The value {amountToWithdraw} exceeds transaction limit: {MaxAmountPerTransaction}.";
}
else
{
lock (balanceLock)
{
if (amountToWithdraw > Amount)
{
message = "Insufficient funds.";
}
else
{
Thread.Sleep(1000);
Amount -= amountToWithdraw;
successful = true;
balanceAfter = Amount;
}
}
}
return new TransactionStatus()
{
Successful = successful, Message = message, BalanceBefore = balanceBefore, BalanceAfter = balanceAfter
};
}
public struct TransactionStatus
{
public bool Successful;
public string Message;
public int BalanceBefore;
public int BalanceAfter;
}
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