c# multithreading and resource locks

me_ said:
I noticed that in your method, you aren't closing the StreamWriter with .Close method after writing. That means you are leaving it open for the garbage collector to finalize and close the file which could lead to intermittent blocking.
Click to expand...

"using" is sugar for try/finally for objects that implement `IDisposable`

Code: 
using (StreamWriter sw = File.CreateText(filepath))
{
     sw.WriteLine(message);
}

results it the following intermediate code

Code: 
StreamWriter sw = File.CreateText(filepath)
try 
{
     sw.WriteLine(message);
}
finally
{
    sw.Dispose();
}
 
_kabal_ said:
"using" is sugar for try/finally for objects that implement `IDisposable`

Code: 
using (StreamWriter sw = File.CreateText(filepath))
{
     sw.WriteLine(message);
}

results it the following intermediate code

Code: 
StreamWriter sw = File.CreateText(filepath)
try
{
     sw.WriteLine(message);
}
finally
{
    sw.Dispose();
}
Click to expand...
Correct.. With .NET6 you also do not need the braces around the usage. Disposal will happen when variable goes out of scope. Removes a bit of clutter.
 
_kabal_ said:
"using" is sugar for try/finally for objects that implement `IDisposable`

Code: 
using (StreamWriter sw = File.CreateText(filepath))
{
     sw.WriteLine(message);
}

results it the following intermediate code

Code: 
StreamWriter sw = File.CreateText(filepath)
try
{
     sw.WriteLine(message);
}
finally
{
    sw.Dispose();
}
Click to expand...
Even shorter:

using SqlConnection sqlConnection = new (connString);
 
_kabal_ said:
"using" is sugar for try/finally for objects that implement `IDisposable`

Code: 
using (StreamWriter sw = File.CreateText(filepath))
{
     sw.WriteLine(message);
}

results it the following intermediate code

Code: 
StreamWriter sw = File.CreateText(filepath)
try
{
     sw.WriteLine(message);
}
finally
{
    sw.Dispose();
}
Click to expand...

Yeah, sorry, I missed the using statement when reading it.
 
Benedict A55h0le said:
File read and write operations is IO intensive so async and await must be used.
Click to expand...
Async I get, but why await ? It will cause a wait, blocking the thread which is calling the method (and has further important code which must execute asap) to write to the log until others are done. I don't want the thread to block.
 
etienne_marais said:
Async I get, but why await ? It will cause a wait, blocking the thread which is calling the method (and has further important code which must execute asap) to write to the log until others are done. I don't want the thread to block.
Click to expand...
As far as I know and read, async and await should always go together, and should be used for all IO operations. I think you kind of have it wrong way round, not using await will "hog" the thread, and using it will put the thread back in the thread pool to be available for other things.
 
As mentioned I have a static class Program and within it a static method to write to files.

I assumed a variable declared in the static method to write the files will automatically be static as well.

I used Object locker = new Object() within the method.

I used lock(locker) around the code using the file/streamwriter.

It did not work.

When I changed Object locker to a global variable within the static class, explicitly defined as static, it worked.

private static Object _locker = new Object();

It worked.

Are variables within a static method within a static class not automatically static then ? (Note, you can't use the static modifier for a variable within a static method). Or are they "kind of" static, just not a single instance ?

Is it because it goes out of scope ? But then two or more threads already within the method should see the same locker ?
 
etienne_marais said:
As mentioned I have a static class Program and within it a static method to write to files.

I assumed a variable declared in the static method to write the files will automatically be static as well.

I used Object locker = new Object() within the method.

I used lock(locker) around the code using the file/streamwriter.

It did not work.

When I changed Object locker to a global variable within the static class, explicitly defined as static, it worked.

private static Object _locker = new Object();

It worked.

Are variables within a static method within a static class not automatically static then ? (Note, you can't use the static modifier for a variable within a static method). Or are they "kind of" static, just not a single instance ?

Is it because it goes out of scope ? But then two or more threads already within the method should see the same locker ?
Click to expand...
I'm not sure of the C# syntax, but in C++, a variable declared inside a static method is local, unless prefixed with static.

godbolt.org

Compiler Explorer - C++ (x86-64 clang 13.0.1)

class A { public: A() {} static void foo() { int a = 0; static int b = 0; a++; b++; printf( "a=%d, b=%d\n", a, b ); } }; int main() { A a; a.foo(); a.foo(); a.foo(); A::foo(); A::foo(); }
godbolt.org godbolt.org
 
cguy said:
I'm not sure of the C# syntax, but in C++, a variable declared inside a static method is local, unless prefixed with static.
Click to expand...
But I thought static is tied to singularity, there are no separate instances and threads entering the static method in the static class use the same (exact) variable despite it being local in scope ? (also in C++ I thought)
 
etienne_marais said:
As mentioned I have a static class Program and within it a static method to write to files.

I assumed a variable declared in the static method to write the files will automatically be static as well.

I used Object locker = new Object() within the method.

I used lock(locker) around the code using the file/streamwriter.

It did not work.

When I changed Object locker to a global variable within the static class, explicitly defined as static, it worked.

private static Object _locker = new Object();

It worked.

Are variables within a static method within a static class not automatically static then ? (Note, you can't use the static modifier for a variable within a static method). Or are they "kind of" static, just not a single instance ?

Is it because it goes out of scope ? But then two or more threads already within the method should see the same locker ?
Click to expand...
Variables in methods/functions have the same scope irregardless if they are static or not

docs.microsoft.com

The lock statement - synchronize access to shared resources - C# reference

Use the C# lock statement to ensure that only a single thread exclusively reads or writes a shared resource, blocking all other threads until it completes.
docs.microsoft.com
 
etienne_marais said:
But I thought static is tied to singularity, there are no separate instances and threads entering the static method in the static class use the same (exact) variable despite it being local in scope ?
Click to expand...
Static on a class method means that the method is class scope rather than object scope (i.e., it can be invoked without a class instance, and cannot access this, or member variables, etc.).

The variables are still locally constructed and destructed inside static members unless declared static (in which case they are constructed upon first invocation).
 
Benedict A55h0le said:
As far as I know and read, async and await should always go together, and should be used for all IO operations. I think you kind of have it wrong way round, not using await will "hog" the thread, and using it will put the thread back in the thread pool to be available for other things.
Click to expand...

As you probably saw from the link you posted, not necessarily. You can use it like EM suggested. There are reasons it shouldn't be done, but I can't remember all of them.
Error handling is one of them, although there are ways around it.
 
cguy said:
That scope refers to where the variables can be accessed from, not the lifetime of the variable.
Click to expand...
The link was more to show how lock works.

Scope was the wrong word :thumbsup:

The point is, there is nothing special about a variable declared inside a static method vs a class method. It’s scope is as expected - it cannot be accessed outside the function, and it’s lifetime is as expected- it’s created on every invocation
 
_kabal_ said:
Variables in methods/functions have the same scope irregardless if they are static or not
Click to expand...
I get that, I thought all threads entering the thread at the same time and seeing the local variable will be looking at the (exact) same thing
_kabal_ said:
docs.microsoft.com

The lock statement - synchronize access to shared resources - C# reference

Use the C# lock statement to ensure that only a single thread exclusively reads or writes a shared resource, blocking all other threads until it completes.
docs.microsoft.com
Click to expand...
 
cguy said:
The variables are still locally constructed and destructed inside static members unless declared static (in which case they are constructed upon first invocation).
Click to expand...
I will go with this then, c# does not allow the static modifier within the static method, so I am assuming it is somehow not Truly static.
 
etienne_marais said:
I will go with this then, c# does not allow the static modifier within the static method, so I am assuming it is somehow not Truly static.
Click to expand...
Seems to work exactly as expected - the same as every other language I have used.

What languages can you define a static variable inside static method?

Why would not just do

Code: 
static object _lock = new Object()

static void MyFunction() {
}

This is how it is/works????
 
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