线程与委托存在什么问题？代码抛出System.ArgumentOutOfRangeException异常

First, let's clean up the code snippet you shared (looks like the third connection string was cut off mid-way, so I'll note that):

ArrayList conarr = new ArrayList(); 
conarr.Add("User ID=sysdba;Password=wrongpass1;" + "Database=C:\\prod\\file.fdb;DataSource=192.168.0.5;Charset=NONE; Connection Timeout=30;Pooling=false;"); 
conarr.Add("User ID=sysdba;Password=wrongpass2;" + "Database=C:\\prod\\file.fdb;DataSource=192.168.0.5;Charset=NONE; Connection Timeout=30;Pooling=false;"); 
conarr.Add("User ID=sysdba;Password=GOODPAS..."); // This string is unclosed—probably a copy-paste truncation, but worth checking in your actual code

Since you mentioned this ties into threads and delegates, here are the most likely culprits behind that System.ArgumentOutOfRangeException:

1. Out-of-Bounds Index Access (Most Common) #

This exception almost always pops up when you try to access a collection element with an index that's outside the valid range (i.e., less than 0 or greater than/equal to conarr.Count). If your thread code uses something like conarr[i], double-check how i is calculated:

• Did you accidentally use <= conarr.Count instead of < conarr.Count in a loop?
• Is i being modified by another thread while your delegate is running?

For example, this mistake would trigger the error instantly:

// Bad loop: i goes up to conarr.Count, which is one past the last valid index
for(int i = 0; i <= conarr.Count; i++) 
{
    var connStr = conarr[i];
    // Delegate/threaded database logic here
}

2. Thread Safety Issues with ArrayList #

ArrayList is not thread-safe. If multiple threads are modifying the list (adding/removing elements) while another thread is reading from it, you can get inconsistent Count values. For example:

• Thread A starts adding a new element to conarr
• Thread B reads conarr.Count right before Thread A finishes, uses that number to set its loop bounds
• Thread A finishes adding, so conarr.Count is now higher—but Thread B's loop might try to access an index that didn't exist when it started, or vice versa.

Fix this by either using a thread-safe collection like ConcurrentBag (from System.Collections.Concurrent) or wrapping all access/modifications to conarr in a lock block:

lock(conarr)
{
    // Add elements or access indices here
}

3. Closure Capture Bug in Delegates #

If you're using delegates inside a loop (like with ThreadPool.QueueUserWorkItem or Task.Run), you might be falling victim to a common closure gotcha. When you capture a loop variable directly in a delegate, the delegate holds a reference to the variable—not its value at the time the delegate was created.

Here's the problematic code:

// Bad: The delegate captures a reference to i, not its current value
for(int i = 0; i < conarr.Count; i++)
{
    ThreadPool.QueueUserWorkItem(state => 
    {
        var connStr = conarr[i]; // By the time the thread runs, i might be conarr.Count
        // Database logic here
    });
}

By the time the thread executes, the loop has already finished, so i equals conarr.Count—hence the index out of range. Fix this by creating a temporary variable inside the loop to capture the current index value:

// Good: Capture a copy of i in tempIndex
for(int i = 0; i < conarr.Count; i++)
{
    int tempIndex = i;
    ThreadPool.QueueUserWorkItem(state => 
    {
        var connStr = conarr[tempIndex];
        // Database logic here
    });
}

4. Unclosed String (Syntax Error) #

The third connection string in your snippet is unclosed ("User ID=sysdba;Password=GOODPAS..."). If this is how your actual code looks, it would cause a compile error before even hitting the runtime exception. Make sure all string literals are properly closed with a quote.

Quick Fix Checklist #

1. Verify all index accesses to conarr stay within 0 to conarr.Count - 1
2. Switch to a thread-safe collection or add locks if multiple threads touch the list
3. Fix closure capture issues by using temporary variables in loops
4. Double-check all string syntax for unclosed literals

内容的提问来源于stack exchange，提问作者user2265690