public
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EnyimMemcached
3 participants
What kind of exception did you get? Some exceptions MUST be thrown, but it's possible that the exception you encountered was a bug coming from other parts of the code, this doing a generic catch is not a good solution.
Also, could you please reformat your code to match the rest of the files, so i do not have to commit a "cosmetic changes" patch?
(tabs, instead of spaces; follow indentation, etc.)
Hello, everybody.
How to distinguish whether the TryGet returns false because of absense of key in the cache or because of the communication failure?
TryGet should throws MemcachedClientException in case of communication failures.
My particular problem was with a byte-based enum. Such a value successfully serializes but upon deserialization throws an error. As I think about it more, I start realizing that TryGet which never throws may be not the best idea because it would mask situation like mine and but would remain unnoticed for some time.
May be problem lays in associations: I expected it to behave like *.TryParse which would swallow exceptions otherwise thrown by Parse.
Probably the serialization exceptions should escape from the transcoder which would handle your particular case as well.
I'll give it a try to see how it can be solved because it must be configurable to be backwards compatible with previous versions.
Fixed signature key according to your recommendations. Thanks for review!
Will rework those series of patches into smaller ones.
vchekan
closed this
Showing 2 changed files with 38 additions and 17 deletions. Show Diff Stats
@@ -102,9 +102,9 @@ private static IMemcachedClientConfiguration GetSection(string sectionName) |
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| 102 | 102 |
/// <returns>The retrieved item, or <value>null</value> if the key was not found.</returns> |
| 103 | 103 |
public object Get(string key) |
| 104 | 104 |
{
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- object tmp; |
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- |
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- return this.TryGet(key, out tmp) ? tmp : null; |
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+ object tmp; |
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+ ulong cas; |
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+ return this.PerformTryGet(key, out cas, out tmp) ? tmp : null; |
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| 108 | 108 |
} |
| 109 | 109 |
|
| 110 | 110 |
/// <summary> |
@@ -114,9 +114,9 @@ public object Get(string key) |
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| 114 | 114 |
/// <returns>The retrieved item, or <value>default(T)</value> if the key was not found.</returns> |
| 115 | 115 |
public T Get<T>(string key) |
| 116 | 116 |
{
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- object tmp; |
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- |
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- return TryGet(key, out tmp) ? (T)tmp : default(T); |
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+ object tmp; |
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+ ulong cas; |
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+ return PerformTryGet(key, out cas, out tmp) ? (T)tmp : default(T); |
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| 120 | 120 |
} |
| 121 | 121 |
|
| 122 | 122 |
/// <summary> |
@@ -126,10 +126,18 @@ public T Get<T>(string key) |
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| 126 | 126 |
/// <param name="value">The retrieved item or null if not found.</param> |
| 127 | 127 |
/// <returns>The <value>true</value> if the item was successfully retrieved.</returns> |
| 128 | 128 |
public bool TryGet(string key, out object value) |
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- {
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- ulong cas = 0; |
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- |
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- return this.PerformTryGet(key, out cas, out value); |
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+ {
|
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+ try |
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+ {
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+ ulong cas; |
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+ return this.PerformTryGet(key, out cas, out value); |
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+ } |
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+ catch(Exception e) |
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+ {
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+ log.Error("TryGet", e);
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+ value = null; |
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+ return false; |
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+ } |
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| 133 | 141 |
} |
| 134 | 142 |
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| 135 | 143 |
public CasResult<object> GetWithCas(string key) |
@@ -149,13 +157,20 @@ public CasResult<T> GetWithCas<T>(string key) |
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| 149 | 157 |
public bool TryGetWithCas(string key, out CasResult<object> value) |
| 150 | 158 |
{
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| 151 | 159 |
object tmp; |
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- ulong cas; |
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- |
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- var retval = this.PerformTryGet(key, out cas, out tmp); |
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- |
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- value = new CasResult<object> { Cas = cas, Result = tmp };
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- |
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- return retval; |
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+ ulong cas; |
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+ |
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+ try |
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+ {
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+ var retval = this.PerformTryGet(key, out cas, out tmp); |
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+ value = new CasResult<object> {Cas = cas, Result = tmp};
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+ return retval; |
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+ } |
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+ catch (Exception e) |
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+ {
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+ log.Error("TryGet", e);
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+ value = default(CasResult<object>); |
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+ return false; |
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+ } |
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| 159 | 174 |
} |
| 160 | 175 |
|
| 161 | 176 |
protected virtual bool PerformTryGet(string key, out ulong cas, out object value) |
@@ -30,6 +30,12 @@ |
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| 30 | 30 |
<DelaySign>true</DelaySign> |
| 31 | 31 |
</PropertyGroup> |
| 32 | 32 |
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+ <!-- if private signature is supplied --> |
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+ <PropertyGroup Condition=" Exists('..\private.snk') ">
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+ <AssemblyOriginatorKeyFile>..\private.snk</AssemblyOriginatorKeyFile> |
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+ <DelaySign>false</DelaySign> |
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+ </PropertyGroup> |
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+ |
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<!-- sign the assembly using the specified key file containing both the private and public keys --> |
| 34 | 40 |
<PropertyGroup Condition=" '$(PrivateKeyPath)' != '' "> |
| 35 | 41 |
<AssemblyOriginatorKeyFile>$(PrivateKeyPath)</AssemblyOriginatorKeyFile> |
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I would expect TryGet to never fail and return "false" either when cache miss or exception happen.
But it is not so. No exception is handled by TryGet.
This leads to "poisoned cache" situation. If I save in cache some value which throws an exception when deserializing, it will never be replaced by a good value in this client code (pseudocode):
if(!_cache.TryGet())
_cache.Set(GetValueExpensive())
Instead much more heavier approach needs to be taken with wrapping TryGet into exception and handling it.
Unfortunately "poisoned cache" situation happens not very often and very likely won't be detected in QA cycle. As result it encourage writing a code which is not reliable.
Proposed patch mitigates the issue by wrapping Try* methods implementation into try-catch clause.