Will lock prevent changes done via reflection
Assume a class SomeClass with private static field like this. The access to this field is synchronized using lock.
private static SomeClass _instance
private static object _sync = new object();
public static SomeClass Instance
{
get
{
lock (_sync)
{
if (_instance == null)
{
_instance = Create();
}
return _instance;
}
}
}
When another code from different thread will try to set the value of this variable to e.g. null using reflection, will the lock prevent this and let the reflection call wait until the lock was released?
E.g. something like this:
Type type = typeof(SomeClass);
string fieldName = "_instance";
object value = null;
FieldInfo field = type.GetField(fieldName, true);
field.SetValue(null, value);
c# reflection locking
asked Nov 15 '18 at 15:20
deedee
10.6k32445
|
show 2 more comments
Assume a class SomeClass with private static field like this. The access to this field is synchronized using lock.
private static SomeClass _instance
private static object _sync = new object();
public static SomeClass Instance
{
get
{
lock (_sync)
{
if (_instance == null)
{
_instance = Create();
}
return _instance;
}
}
}
When another code from different thread will try to set the value of this variable to e.g. null using reflection, will the lock prevent this and let the reflection call wait until the lock was released?
E.g. something like this:
Type type = typeof(SomeClass);
string fieldName = "_instance";
object value = null;
FieldInfo field = type.GetField(fieldName, true);
field.SetValue(null, value);
c# reflection locking
asked Nov 15 '18 at 15:20
deedee
10.6k32445
2
the answer here is simply: no
– Daniel A. White
Nov 15 '18 at 15:25
this is a social-engineering problem - catch bad behavior in code reviews.
– Daniel A. White
Nov 15 '18 at 15:25
I think this question at least deserves an answer elaborating on the "why?", the technical, CLR-related reason. Documentation only says, "avoid using the following as lock objects: Type instances, as those might be obtained by thetypeofoperator or reflection" and that's not what OP does.
– dlatikay
Nov 15 '18 at 15:37
lockis collaborative. All code accessing the same protected resources has to be written to follow whatever locking rules you're trying to establish. If someone else writes code that accesses the protected resource(s) but doesn't follow your locking convention, nothing prevents that. How did you imagine that anything else would know, specifically, that_syncand_instanceare related?
– Damien_The_Unbeliever
Nov 15 '18 at 17:44
1
@dee - it's got nothing to do with reflection. If you write another method in this class that accesses the same resource and fails to use the same lock object, that would also compile and run fine and race the same issues
– Damien_The_Unbeliever
Nov 15 '18 at 19:03
|
show 2 more comments
Assume a class SomeClass with private static field like this. The access to this field is synchronized using lock.
private static SomeClass _instance
private static object _sync = new object();
public static SomeClass Instance
{
get
{
lock (_sync)
{
if (_instance == null)
{
_instance = Create();
}
return _instance;
}
}
}
When another code from different thread will try to set the value of this variable to e.g. null using reflection, will the lock prevent this and let the reflection call wait until the lock was released?
E.g. something like this:
Type type = typeof(SomeClass);
string fieldName = "_instance";
object value = null;
FieldInfo field = type.GetField(fieldName, true);
field.SetValue(null, value);
c# reflection locking
asked Nov 15 '18 at 15:20
deedee
10.6k32445
Assume a class SomeClass with private static field like this. The access to this field is synchronized using lock.
private static SomeClass _instance
private static object _sync = new object();
public static SomeClass Instance
{
get
{
lock (_sync)
{
if (_instance == null)
{
_instance = Create();
}
return _instance;
}
}
}
When another code from different thread will try to set the value of this variable to e.g. null using reflection, will the lock prevent this and let the reflection call wait until the lock was released?
E.g. something like this:
Type type = typeof(SomeClass);
string fieldName = "_instance";
object value = null;
FieldInfo field = type.GetField(fieldName, true);
field.SetValue(null, value);
c# reflection locking
c# reflection locking
asked Nov 15 '18 at 15:20
deedee
10.6k32445
asked Nov 15 '18 at 15:20
deedee
10.6k32445
edited Nov 15 '18 at 15:24
dee
asked Nov 15 '18 at 15:20
deedee
10.6k32445
asked Nov 15 '18 at 15:20
deedee
10.6k32445
asked Nov 15 '18 at 15:20
deedee
10.6k32445
10.6k32445
2
the answer here is simply: no
– Daniel A. White
Nov 15 '18 at 15:25
this is a social-engineering problem - catch bad behavior in code reviews.
– Daniel A. White
Nov 15 '18 at 15:25
I think this question at least deserves an answer elaborating on the "why?", the technical, CLR-related reason. Documentation only says, "avoid using the following as lock objects: Type instances, as those might be obtained by thetypeofoperator or reflection" and that's not what OP does.
– dlatikay
Nov 15 '18 at 15:37
lockis collaborative. All code accessing the same protected resources has to be written to follow whatever locking rules you're trying to establish. If someone else writes code that accesses the protected resource(s) but doesn't follow your locking convention, nothing prevents that. How did you imagine that anything else would know, specifically, that_syncand_instanceare related?
– Damien_The_Unbeliever
Nov 15 '18 at 17:44
1
@dee - it's got nothing to do with reflection. If you write another method in this class that accesses the same resource and fails to use the same lock object, that would also compile and run fine and race the same issues
– Damien_The_Unbeliever
Nov 15 '18 at 19:03
|
show 2 more comments
2
the answer here is simply: no
– Daniel A. White
Nov 15 '18 at 15:25
this is a social-engineering problem - catch bad behavior in code reviews.
– Daniel A. White
Nov 15 '18 at 15:25
I think this question at least deserves an answer elaborating on the "why?", the technical, CLR-related reason. Documentation only says, "avoid using the following as lock objects: Type instances, as those might be obtained by thetypeofoperator or reflection" and that's not what OP does.
– dlatikay
Nov 15 '18 at 15:37
lockis collaborative. All code accessing the same protected resources has to be written to follow whatever locking rules you're trying to establish. If someone else writes code that accesses the protected resource(s) but doesn't follow your locking convention, nothing prevents that. How did you imagine that anything else would know, specifically, that_syncand_instanceare related?
– Damien_The_Unbeliever
Nov 15 '18 at 17:44
1
@dee - it's got nothing to do with reflection. If you write another method in this class that accesses the same resource and fails to use the same lock object, that would also compile and run fine and race the same issues
– Damien_The_Unbeliever
Nov 15 '18 at 19:03
2
2
the answer here is simply: no
– Daniel A. White
Nov 15 '18 at 15:25
the answer here is simply: no
– Daniel A. White
Nov 15 '18 at 15:25
this is a social-engineering problem - catch bad behavior in code reviews.
– Daniel A. White
Nov 15 '18 at 15:25
this is a social-engineering problem - catch bad behavior in code reviews.
– Daniel A. White
Nov 15 '18 at 15:25
I think this question at least deserves an answer elaborating on the "why?", the technical, CLR-related reason. Documentation only says, "avoid using the following as lock objects: Type instances, as those might be obtained by the
typeof operator or reflection" and that's not what OP does.– dlatikay
Nov 15 '18 at 15:37
I think this question at least deserves an answer elaborating on the "why?", the technical, CLR-related reason. Documentation only says, "avoid using the following as lock objects: Type instances, as those might be obtained by the
typeof operator or reflection" and that's not what OP does.– dlatikay
Nov 15 '18 at 15:37
lock is collaborative. All code accessing the same protected resources has to be written to follow whatever locking rules you're trying to establish. If someone else writes code that accesses the protected resource(s) but doesn't follow your locking convention, nothing prevents that. How did you imagine that anything else would know, specifically, that _sync and _instance are related?– Damien_The_Unbeliever
Nov 15 '18 at 17:44
lock is collaborative. All code accessing the same protected resources has to be written to follow whatever locking rules you're trying to establish. If someone else writes code that accesses the protected resource(s) but doesn't follow your locking convention, nothing prevents that. How did you imagine that anything else would know, specifically, that _sync and _instance are related?– Damien_The_Unbeliever
Nov 15 '18 at 17:44
1
1
@dee - it's got nothing to do with reflection. If you write another method in this class that accesses the same resource and fails to use the same lock object, that would also compile and run fine and race the same issues
– Damien_The_Unbeliever
Nov 15 '18 at 19:03
@dee - it's got nothing to do with reflection. If you write another method in this class that accesses the same resource and fails to use the same lock object, that would also compile and run fine and race the same issues
– Damien_The_Unbeliever
Nov 15 '18 at 19:03
|
show 2 more comments
1 Answer
1
active
oldest
votes
No, lock will not prevent any access that does not go through locking the same resource. Since reflection will not go through lock, you will get race conditions.
Here is (slightly different from your code but nontheless doing same thing) what I mean→
void SetOne(){
lock (_sync){
critical_element = SOME_VALUE;
}
}
void SetTwo(){
critical_element = SOME_ANOTHER_VALUE;
}
Above definitely has race conditions.
Here is my understanding behind the OP's question. I think OP wants to use Singleton pattern and here is a very nice and thread safe implementation. You do not need to deal with locks either. However, some bad users might still set the backing field using reflection.
public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy = new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance { get { return lazy.Value; } }
private Singleton(){}
}
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
Thank you for your answer! I understood that the lock is effective only for calls which go through the normal access, but with reflection there the value is changed directly. That was my question, I was not sure, how the locking works. The singleton with Lazy of T is cool, thanks as well.
– dee
Nov 19 '18 at 19:41
add a comment |
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1 Answer
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oldest
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oldest
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oldest
votes
No, lock will not prevent any access that does not go through locking the same resource. Since reflection will not go through lock, you will get race conditions.
Here is (slightly different from your code but nontheless doing same thing) what I mean→
void SetOne(){
lock (_sync){
critical_element = SOME_VALUE;
}
}
void SetTwo(){
critical_element = SOME_ANOTHER_VALUE;
}
Above definitely has race conditions.
Here is my understanding behind the OP's question. I think OP wants to use Singleton pattern and here is a very nice and thread safe implementation. You do not need to deal with locks either. However, some bad users might still set the backing field using reflection.
public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy = new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance { get { return lazy.Value; } }
private Singleton(){}
}
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
Thank you for your answer! I understood that the lock is effective only for calls which go through the normal access, but with reflection there the value is changed directly. That was my question, I was not sure, how the locking works. The singleton with Lazy of T is cool, thanks as well.
– dee
Nov 19 '18 at 19:41
add a comment |
No, lock will not prevent any access that does not go through locking the same resource. Since reflection will not go through lock, you will get race conditions.
Here is (slightly different from your code but nontheless doing same thing) what I mean→
void SetOne(){
lock (_sync){
critical_element = SOME_VALUE;
}
}
void SetTwo(){
critical_element = SOME_ANOTHER_VALUE;
}
Above definitely has race conditions.
Here is my understanding behind the OP's question. I think OP wants to use Singleton pattern and here is a very nice and thread safe implementation. You do not need to deal with locks either. However, some bad users might still set the backing field using reflection.
public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy = new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance { get { return lazy.Value; } }
private Singleton(){}
}
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
Thank you for your answer! I understood that the lock is effective only for calls which go through the normal access, but with reflection there the value is changed directly. That was my question, I was not sure, how the locking works. The singleton with Lazy of T is cool, thanks as well.
– dee
Nov 19 '18 at 19:41
add a comment |
No, lock will not prevent any access that does not go through locking the same resource. Since reflection will not go through lock, you will get race conditions.
Here is (slightly different from your code but nontheless doing same thing) what I mean→
void SetOne(){
lock (_sync){
critical_element = SOME_VALUE;
}
}
void SetTwo(){
critical_element = SOME_ANOTHER_VALUE;
}
Above definitely has race conditions.
Here is my understanding behind the OP's question. I think OP wants to use Singleton pattern and here is a very nice and thread safe implementation. You do not need to deal with locks either. However, some bad users might still set the backing field using reflection.
public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy = new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance { get { return lazy.Value; } }
private Singleton(){}
}
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
No, lock will not prevent any access that does not go through locking the same resource. Since reflection will not go through lock, you will get race conditions.
Here is (slightly different from your code but nontheless doing same thing) what I mean→
void SetOne(){
lock (_sync){
critical_element = SOME_VALUE;
}
}
void SetTwo(){
critical_element = SOME_ANOTHER_VALUE;
}
Above definitely has race conditions.
Here is my understanding behind the OP's question. I think OP wants to use Singleton pattern and here is a very nice and thread safe implementation. You do not need to deal with locks either. However, some bad users might still set the backing field using reflection.
public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy = new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance { get { return lazy.Value; } }
private Singleton(){}
}
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
answered Nov 16 '18 at 8:00
Hasan Emrah SüngüHasan Emrah Süngü
1,698322
1,698322
Thank you for your answer! I understood that the lock is effective only for calls which go through the normal access, but with reflection there the value is changed directly. That was my question, I was not sure, how the locking works. The singleton with Lazy of T is cool, thanks as well.
– dee
Nov 19 '18 at 19:41
add a comment |
Thank you for your answer! I understood that the lock is effective only for calls which go through the normal access, but with reflection there the value is changed directly. That was my question, I was not sure, how the locking works. The singleton with Lazy of T is cool, thanks as well.
– dee
Nov 19 '18 at 19:41
Thank you for your answer! I understood that the lock is effective only for calls which go through the normal access, but with reflection there the value is changed directly. That was my question, I was not sure, how the locking works. The singleton with Lazy of T is cool, thanks as well.
– dee
Nov 19 '18 at 19:41
Thank you for your answer! I understood that the lock is effective only for calls which go through the normal access, but with reflection there the value is changed directly. That was my question, I was not sure, how the locking works. The singleton with Lazy of T is cool, thanks as well.
– dee
Nov 19 '18 at 19:41
add a comment |
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2
the answer here is simply: no
– Daniel A. White
Nov 15 '18 at 15:25
this is a social-engineering problem - catch bad behavior in code reviews.
– Daniel A. White
Nov 15 '18 at 15:25
I think this question at least deserves an answer elaborating on the "why?", the technical, CLR-related reason. Documentation only says, "avoid using the following as lock objects: Type instances, as those might be obtained by the
typeofoperator or reflection" and that's not what OP does.– dlatikay
Nov 15 '18 at 15:37
lockis collaborative. All code accessing the same protected resources has to be written to follow whatever locking rules you're trying to establish. If someone else writes code that accesses the protected resource(s) but doesn't follow your locking convention, nothing prevents that. How did you imagine that anything else would know, specifically, that_syncand_instanceare related?– Damien_The_Unbeliever
Nov 15 '18 at 17:44
1
@dee - it's got nothing to do with reflection. If you write another method in this class that accesses the same resource and fails to use the same lock object, that would also compile and run fine and race the same issues
– Damien_The_Unbeliever
Nov 15 '18 at 19:03