Safely Initialising a static variable to a file
2
$begingroup$
This might appear to be a trivial task, but I think it's not the case. My code originally looked like this:
class DataSetToPdf
{
static byte F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
// Code which uses F1
}
}
Util.GetFile simply reads the file and returns an array of bytes. For completeness, here it is:
class Util
{
public static byte GetFile( String path )
{
IO.MemoryStream ms = new IO.MemoryStream();
using( IO.FileStream f = IO.File.OpenRead( path) )
{
f.CopyTo( ms );
}
return ms.ToArray();
}
}
However, when using DataSetToPdf in a multi-threaded environment (IIS), I was sometimes ( but not always ) getting mysterious null reference exceptions, which I could not easily debug. However, what I believe what was happening is that the static method could be called before the initialisation is complete. Instead what appears to be is necessary is this:
class DataSetToPdf
{
static System.Object Locker = new System.Object();
static byte F1;
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
lock( Locker )
{
if ( F1 == null )
{
F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
}
}
// Code which uses F1
}
}
Please review my updated code, was it wrong before, is it right now?
c#
edited 2 mins ago
t3chb0t
34.4k748118
asked 13 hours ago
George BarwoodGeorge Barwood
4079
$endgroup$
|
show 1 more comment
2
$begingroup$
This might appear to be a trivial task, but I think it's not the case. My code originally looked like this:
class DataSetToPdf
{
static byte F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
// Code which uses F1
}
}
Util.GetFile simply reads the file and returns an array of bytes. For completeness, here it is:
class Util
{
public static byte GetFile( String path )
{
IO.MemoryStream ms = new IO.MemoryStream();
using( IO.FileStream f = IO.File.OpenRead( path) )
{
f.CopyTo( ms );
}
return ms.ToArray();
}
}
However, when using DataSetToPdf in a multi-threaded environment (IIS), I was sometimes ( but not always ) getting mysterious null reference exceptions, which I could not easily debug. However, what I believe what was happening is that the static method could be called before the initialisation is complete. Instead what appears to be is necessary is this:
class DataSetToPdf
{
static System.Object Locker = new System.Object();
static byte F1;
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
lock( Locker )
{
if ( F1 == null )
{
F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
}
}
// Code which uses F1
}
}
Please review my updated code, was it wrong before, is it right now?
c#
edited 2 mins ago
t3chb0t
34.4k748118
asked 13 hours ago
George BarwoodGeorge Barwood
4079
$endgroup$
2
$begingroup$
MemoryStreamis also anIDisposable-implementing class (it descends fromStream) and should be wrapped in ausingconstruct just likeFileStreamis.
$endgroup$
– Jesse C. Slicer
13 hours ago
1
$begingroup$
What was the null reference exception?F1could never be null, becauseMemoryStream.ToArray()never returns null. Ideally,F1should bereadonly, so I guess it's possible something else is setting it to null. My guess is the exception is unrelated.
$endgroup$
– Brad M
12 hours ago
2
$begingroup$
Also,File.ReadAllBytes()should be able to do what you want without the intermediate copy to memory stream.
$endgroup$
– Jesse C. Slicer
12 hours ago
$begingroup$
@BradM F1 was null because it hadn't YET been initialised. C# doesn't guarantee that initialisation of static members completes before members are called in a multi-threaded environment ( which caught me out ). I believe it can only happen when the initialisation is delayed by blocking, in this case an IO operation.
$endgroup$
– George Barwood
12 hours ago
1
$begingroup$
@GeorgeBarwood Thats not true to my knowledge. Static fields are guaranteed to be initalized before first usage.
$endgroup$
– Brad M
12 hours ago
|
show 1 more comment
2
2
2
$begingroup$
This might appear to be a trivial task, but I think it's not the case. My code originally looked like this:
class DataSetToPdf
{
static byte F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
// Code which uses F1
}
}
Util.GetFile simply reads the file and returns an array of bytes. For completeness, here it is:
class Util
{
public static byte GetFile( String path )
{
IO.MemoryStream ms = new IO.MemoryStream();
using( IO.FileStream f = IO.File.OpenRead( path) )
{
f.CopyTo( ms );
}
return ms.ToArray();
}
}
However, when using DataSetToPdf in a multi-threaded environment (IIS), I was sometimes ( but not always ) getting mysterious null reference exceptions, which I could not easily debug. However, what I believe what was happening is that the static method could be called before the initialisation is complete. Instead what appears to be is necessary is this:
class DataSetToPdf
{
static System.Object Locker = new System.Object();
static byte F1;
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
lock( Locker )
{
if ( F1 == null )
{
F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
}
}
// Code which uses F1
}
}
Please review my updated code, was it wrong before, is it right now?
c#
edited 2 mins ago
t3chb0t
34.4k748118
asked 13 hours ago
George BarwoodGeorge Barwood
4079
$endgroup$
This might appear to be a trivial task, but I think it's not the case. My code originally looked like this:
class DataSetToPdf
{
static byte F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
// Code which uses F1
}
}
Util.GetFile simply reads the file and returns an array of bytes. For completeness, here it is:
class Util
{
public static byte GetFile( String path )
{
IO.MemoryStream ms = new IO.MemoryStream();
using( IO.FileStream f = IO.File.OpenRead( path) )
{
f.CopyTo( ms );
}
return ms.ToArray();
}
}
However, when using DataSetToPdf in a multi-threaded environment (IIS), I was sometimes ( but not always ) getting mysterious null reference exceptions, which I could not easily debug. However, what I believe what was happening is that the static method could be called before the initialisation is complete. Instead what appears to be is necessary is this:
class DataSetToPdf
{
static System.Object Locker = new System.Object();
static byte F1;
public static void Go( Data.DataSet ds, int ix, System.IO.Stream output )
{
lock( Locker )
{
if ( F1 == null )
{
F1 = Util.GetFile( "C:PdfFilesFreeSans.ttf" );
}
}
// Code which uses F1
}
}
Please review my updated code, was it wrong before, is it right now?
c#
c#
edited 2 mins ago
t3chb0t
34.4k748118
asked 13 hours ago
George BarwoodGeorge Barwood
4079
edited 2 mins ago
t3chb0t
34.4k748118
asked 13 hours ago
George BarwoodGeorge Barwood
4079
edited 2 mins ago
t3chb0t
34.4k748118
edited 2 mins ago
t3chb0t
34.4k748118
edited 2 mins ago
t3chb0t
34.4k748118
34.4k748118
asked 13 hours ago
George BarwoodGeorge Barwood
4079
asked 13 hours ago
George BarwoodGeorge Barwood
4079
asked 13 hours ago
George BarwoodGeorge Barwood
4079
4079
2
$begingroup$
MemoryStreamis also anIDisposable-implementing class (it descends fromStream) and should be wrapped in ausingconstruct just likeFileStreamis.
$endgroup$
– Jesse C. Slicer
13 hours ago
1
$begingroup$
What was the null reference exception?F1could never be null, becauseMemoryStream.ToArray()never returns null. Ideally,F1should bereadonly, so I guess it's possible something else is setting it to null. My guess is the exception is unrelated.
$endgroup$
– Brad M
12 hours ago
2
$begingroup$
Also,File.ReadAllBytes()should be able to do what you want without the intermediate copy to memory stream.
$endgroup$
– Jesse C. Slicer
12 hours ago
$begingroup$
@BradM F1 was null because it hadn't YET been initialised. C# doesn't guarantee that initialisation of static members completes before members are called in a multi-threaded environment ( which caught me out ). I believe it can only happen when the initialisation is delayed by blocking, in this case an IO operation.
$endgroup$
– George Barwood
12 hours ago
1
$begingroup$
@GeorgeBarwood Thats not true to my knowledge. Static fields are guaranteed to be initalized before first usage.
$endgroup$
– Brad M
12 hours ago
|
show 1 more comment
2
$begingroup$
MemoryStreamis also anIDisposable-implementing class (it descends fromStream) and should be wrapped in ausingconstruct just likeFileStreamis.
$endgroup$
– Jesse C. Slicer
13 hours ago
1
$begingroup$
What was the null reference exception?F1could never be null, becauseMemoryStream.ToArray()never returns null. Ideally,F1should bereadonly, so I guess it's possible something else is setting it to null. My guess is the exception is unrelated.
$endgroup$
– Brad M
12 hours ago
2
$begingroup$
Also,File.ReadAllBytes()should be able to do what you want without the intermediate copy to memory stream.
$endgroup$
– Jesse C. Slicer
12 hours ago
$begingroup$
@BradM F1 was null because it hadn't YET been initialised. C# doesn't guarantee that initialisation of static members completes before members are called in a multi-threaded environment ( which caught me out ). I believe it can only happen when the initialisation is delayed by blocking, in this case an IO operation.
$endgroup$
– George Barwood
12 hours ago
1
$begingroup$
@GeorgeBarwood Thats not true to my knowledge. Static fields are guaranteed to be initalized before first usage.
$endgroup$
– Brad M
12 hours ago
2
2
$begingroup$
MemoryStream is also an IDisposable-implementing class (it descends from Stream) and should be wrapped in a using construct just like FileStream is.$endgroup$
– Jesse C. Slicer
13 hours ago
$begingroup$
MemoryStream is also an IDisposable-implementing class (it descends from Stream) and should be wrapped in a using construct just like FileStream is.$endgroup$
– Jesse C. Slicer
13 hours ago
1
1
$begingroup$
What was the null reference exception?
F1 could never be null, because MemoryStream.ToArray() never returns null. Ideally, F1 should be readonly, so I guess it's possible something else is setting it to null. My guess is the exception is unrelated.$endgroup$
– Brad M
12 hours ago
$begingroup$
What was the null reference exception?
F1 could never be null, because MemoryStream.ToArray() never returns null. Ideally, F1 should be readonly, so I guess it's possible something else is setting it to null. My guess is the exception is unrelated.$endgroup$
– Brad M
12 hours ago
2
2
$begingroup$
Also,
File.ReadAllBytes() should be able to do what you want without the intermediate copy to memory stream.$endgroup$
– Jesse C. Slicer
12 hours ago
$begingroup$
Also,
File.ReadAllBytes() should be able to do what you want without the intermediate copy to memory stream.$endgroup$
– Jesse C. Slicer
12 hours ago
$begingroup$
@BradM F1 was null because it hadn't YET been initialised. C# doesn't guarantee that initialisation of static members completes before members are called in a multi-threaded environment ( which caught me out ). I believe it can only happen when the initialisation is delayed by blocking, in this case an IO operation.
$endgroup$
– George Barwood
12 hours ago
$begingroup$
@BradM F1 was null because it hadn't YET been initialised. C# doesn't guarantee that initialisation of static members completes before members are called in a multi-threaded environment ( which caught me out ). I believe it can only happen when the initialisation is delayed by blocking, in this case an IO operation.
$endgroup$
– George Barwood
12 hours ago
1
1
$begingroup$
@GeorgeBarwood Thats not true to my knowledge. Static fields are guaranteed to be initalized before first usage.
$endgroup$
– Brad M
12 hours ago
$begingroup$
@GeorgeBarwood Thats not true to my knowledge. Static fields are guaranteed to be initalized before first usage.
$endgroup$
– Brad M
12 hours ago
|
show 1 more comment
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2
$begingroup$
MemoryStreamis also anIDisposable-implementing class (it descends fromStream) and should be wrapped in ausingconstruct just likeFileStreamis.$endgroup$
– Jesse C. Slicer
13 hours ago
1
$begingroup$
What was the null reference exception?
F1could never be null, becauseMemoryStream.ToArray()never returns null. Ideally,F1should bereadonly, so I guess it's possible something else is setting it to null. My guess is the exception is unrelated.$endgroup$
– Brad M
12 hours ago
2
$begingroup$
Also,
File.ReadAllBytes()should be able to do what you want without the intermediate copy to memory stream.$endgroup$
– Jesse C. Slicer
12 hours ago
$begingroup$
@BradM F1 was null because it hadn't YET been initialised. C# doesn't guarantee that initialisation of static members completes before members are called in a multi-threaded environment ( which caught me out ). I believe it can only happen when the initialisation is delayed by blocking, in this case an IO operation.
$endgroup$
– George Barwood
12 hours ago
1
$begingroup$
@GeorgeBarwood Thats not true to my knowledge. Static fields are guaranteed to be initalized before first usage.
$endgroup$
– Brad M
12 hours ago