public void StressTest()
{
var helper = new PrnHelper(new QuadraticResidueHelper());
var generatedPrns = new HashSet <string>();
var context = new WeeeContext(userContext, eventDispatcher);
uint seed = (uint)GetCurrentSeed(context);
var components = new PrnAsComponents(seed);
// be careful how high you go with this limit or generatedPrns will fill up
// and your computer will get stuck in page-fault limbo
const int Limit = int.MaxValue / 100;
for (int ii = 0; ii < Limit; ii++)
{
if (ii % (Limit / 10) == 0)
{
Debug.WriteLine("Done another ten per cent...");
}
var resultingPrn = helper.CreateUniqueRandomVersionOfPrn(components);
Assert.False(generatedPrns.Contains(resultingPrn),
string.Format(
"{0} was generated twice but is supposed to be unique for a very large range of seed values",
resultingPrn));
generatedPrns.Add(resultingPrn);
seed = components.ToSeedValue() + 1;
components = new PrnAsComponents(seed);
}
}
public void PrnFromSeed_PassedZero_RecomputedSeedValueEqualsZero()
{
const uint Value = 0;
PrnAsComponents prnAsComponents = new PrnAsComponents(Value);
uint seedFromPrn = prnAsComponents.ToSeedValue();
Assert.Equal(Value, seedFromPrn);
}
public void PrnFromSeed_PassedZero_RecomputedSeedValueEqualsZero()
{
const uint Value = 0;
PrnAsComponents prnAsComponents = new PrnAsComponents(Value);
uint seedFromPrn = prnAsComponents.ToSeedValue();
Assert.Equal(Value, seedFromPrn);
}
public void PrnFromSeed_PassedValueOutOfRange_RecomputedSeedValueIsInRange()
{
const uint Value = 9967;
const uint NextValueInRange = 65536;
PrnAsComponents prnAsComponents = new PrnAsComponents(Value);
uint seedFromPrn = prnAsComponents.ToSeedValue();
Assert.Equal(NextValueInRange, seedFromPrn);
}
public void PrnFromSeed_PassedValueOutOfRange_RecomputedSeedValueIsInRange()
{
const uint Value = 9967;
const uint NextValueInRange = 65536;
PrnAsComponents prnAsComponents = new PrnAsComponents(Value);
uint seedFromPrn = prnAsComponents.ToSeedValue();
Assert.Equal(NextValueInRange, seedFromPrn);
}
private long ExpectedSeedAfterThisXml(string xml, long initialSeed)
{
schemeType parsedXml = ParseXml(xml);
uint expectedSeed = (uint)initialSeed;
for (int ii = 0; ii < parsedXml.producerList.Count(p => p.status == statusType.I); ii++)
{
expectedSeed = new PrnAsComponents(expectedSeed + 1).ToSeedValue();
}
return(expectedSeed);
}
/// <summary>
/// Generates unique, pseudorandom PRNs with minimal database interaction.
/// Works by:
/// a) uniquely mapping each unsigned integer to another pseudorandom unsigned integer
/// b) uniquely mapping each unsigned integer to a specific PRN
/// Combining those two mappings, and using a sequential seed, we can obtain pseudorandom PRNs
/// with assurance that we will not repeat ourselves for a very, very long time.
/// </summary>
/// <param name="context">The database context</param>
/// <param name="numberOfPrnsNeeded">A non-negative integer</param>
/// <returns></returns>
public async Task<Queue<string>> ComputePrns(int numberOfPrnsNeeded)
{
bool succeeded = false;
bool retry = false;
IEnumerable<DbEntityEntry> staleValues = null;
List<PrnAsComponents> generatedPrns = new List<PrnAsComponents>();
ExceptionDispatchInfo exceptionDispatchInfo = null;
var prnHelper = new PrnHelper(new QuadraticResidueHelper());
try
{
succeeded = false;
retry = false;
// to avoid concurrency issues, we want to read the latest seed, 'reserve' some PRNs (figuring
// out the resulting final seed as we go), and write the final seed back as quickly as possible
uint originalLatestSeed = (uint)context.SystemData.Select(sd => sd.LatestPrnSeed).First();
uint currentSeed = originalLatestSeed;
for (int ii = 0; ii < numberOfPrnsNeeded; ii++)
{
var prnFromSeed = new PrnAsComponents(currentSeed + 1);
generatedPrns.Add(prnFromSeed);
currentSeed = prnFromSeed.ToSeedValue();
}
// we write back the next acceptable seed to the database, for next time
// since there are some mathematical constraints on the acceptable values
context.SystemData.First().LatestPrnSeed = currentSeed;
await context.SaveChangesAsync();
succeeded = true;
}
catch (DbUpdateConcurrencyException ex)
{
staleValues = ex.Entries;
retry = true;
}
catch (Exception ex)
{
// In .NET 4.5 it is not allowed to use "await" within catch blocks; this forces us to put
// code after the catch block. As a result of that, we don't want to throw un-handled exceptions
// here, so we capture the dispatch info and throw it at the end of this method.
exceptionDispatchInfo = System.Runtime.ExceptionServices.ExceptionDispatchInfo.Capture(ex);
}
if (succeeded)
{
// now we're done with the fairly time sensitive database read/write,
// we can 'randomise' the results at our leisure
return new Queue<string>(generatedPrns.Select(p => prnHelper.CreateUniqueRandomVersionOfPrn(p)));
}
else if (retry)
{
// If we need to retry, we are probably in a race condition with another thread.
// To avoid retrying indefinitely, we'll wait a few milliseconds to get out of sync
// with the other thread.
await Task.Delay(TimeSpan.FromMilliseconds(new Random().Next(100)));
// If the database value for [LatestPrnSeed] was updated between the time we fetched the value
// tried to update it with our new value, we will get a DbConcurrencyException.
// To handle this we will just call this method again until it succeeds.
// However, as dependency injection forces us to reuse the same WeeeContext, the SystemData
// entity will already be attached to the context giving us the same stale value from when it
// was first fetched.
// The DbUpdateConcurrencyException gives us the ability to reload this entity from the database.
foreach (var entry in staleValues)
{
if (entry.Entity is SystemData)
{
await entry.ReloadAsync();
}
}
// Now that we have the latest value loaded, we'll try calling this method again.
return await ComputePrns(numberOfPrnsNeeded);
}
else
{
// Something else bad happened and it's not possible to fix that here.
exceptionDispatchInfo.Throw();
throw new Exception("This will never be thrown.");
}
}
private long ExpectedSeedAfterThisXml(string xml, long initialSeed)
{
schemeType parsedXml = ParseXml(xml);
uint expectedSeed = (uint)initialSeed;
for (int ii = 0; ii < parsedXml.producerList.Count(p => p.status == statusType.I); ii++)
{
expectedSeed = new PrnAsComponents(expectedSeed + 1).ToSeedValue();
}
return expectedSeed;
}
public void StressTest()
{
var helper = new PrnHelper(new QuadraticResidueHelper());
var generatedPrns = new HashSet<string>();
var context = new WeeeContext(userContext, eventDispatcher);
uint seed = (uint)GetCurrentSeed(context);
var components = new PrnAsComponents(seed);
// be careful how high you go with this limit or generatedPrns will fill up
// and your computer will get stuck in page-fault limbo
const int Limit = int.MaxValue / 100;
for (int ii = 0; ii < Limit; ii++)
{
if (ii % (Limit / 10) == 0)
{
Debug.WriteLine("Done another ten per cent...");
}
var resultingPrn = helper.CreateUniqueRandomVersionOfPrn(components);
Assert.False(generatedPrns.Contains(resultingPrn),
string.Format(
"{0} was generated twice but is supposed to be unique for a very large range of seed values",
resultingPrn));
generatedPrns.Add(resultingPrn);
seed = components.ToSeedValue() + 1;
components = new PrnAsComponents(seed);
}
}
/// <summary>
/// Generates unique, pseudorandom PRNs with minimal database interaction.
/// Works by:
/// a) uniquely mapping each unsigned integer to another pseudorandom unsigned integer
/// b) uniquely mapping each unsigned integer to a specific PRN
/// Combining those two mappings, and using a sequential seed, we can obtain pseudorandom PRNs
/// with assurance that we will not repeat ourselves for a very, very long time.
/// </summary>
/// <param name="context">The database context</param>
/// <param name="numberOfPrnsNeeded">A non-negative integer</param>
/// <returns></returns>
public async Task <Queue <string> > ComputePrns(int numberOfPrnsNeeded)
{
bool succeeded = false;
bool retry = false;
IEnumerable <DbEntityEntry> staleValues = null;
List <PrnAsComponents> generatedPrns = new List <PrnAsComponents>();
ExceptionDispatchInfo exceptionDispatchInfo = null;
var prnHelper = new PrnHelper(new QuadraticResidueHelper());
try
{
succeeded = false;
retry = false;
// to avoid concurrency issues, we want to read the latest seed, 'reserve' some PRNs (figuring
// out the resulting final seed as we go), and write the final seed back as quickly as possible
uint originalLatestSeed = (uint)context.SystemData.Select(sd => sd.LatestPrnSeed).First();
uint currentSeed = originalLatestSeed;
for (int ii = 0; ii < numberOfPrnsNeeded; ii++)
{
var prnFromSeed = new PrnAsComponents(currentSeed + 1);
generatedPrns.Add(prnFromSeed);
currentSeed = prnFromSeed.ToSeedValue();
}
// we write back the next acceptable seed to the database, for next time
// since there are some mathematical constraints on the acceptable values
context.SystemData.First().LatestPrnSeed = currentSeed;
await context.SaveChangesAsync();
succeeded = true;
}
catch (DbUpdateConcurrencyException ex)
{
staleValues = ex.Entries;
retry = true;
}
catch (Exception ex)
{
// In .NET 4.5 it is not allowed to use "await" within catch blocks; this forces us to put
// code after the catch block. As a result of that, we don't want to throw un-handled exceptions
// here, so we capture the dispatch info and throw it at the end of this method.
exceptionDispatchInfo = System.Runtime.ExceptionServices.ExceptionDispatchInfo.Capture(ex);
}
if (succeeded)
{
// now we're done with the fairly time sensitive database read/write,
// we can 'randomise' the results at our leisure
return(new Queue <string>(generatedPrns.Select(p => prnHelper.CreateUniqueRandomVersionOfPrn(p))));
}
else if (retry)
{
// If we need to retry, we are probably in a race condition with another thread.
// To avoid retrying indefinitely, we'll wait a few milliseconds to get out of sync
// with the other thread.
await Task.Delay(TimeSpan.FromMilliseconds(new Random().Next(100)));
// If the database value for [LatestPrnSeed] was updated between the time we fetched the value
// tried to update it with our new value, we will get a DbConcurrencyException.
// To handle this we will just call this method again until it succeeds.
// However, as dependency injection forces us to reuse the same WeeeContext, the SystemData
// entity will already be attached to the context giving us the same stale value from when it
// was first fetched.
// The DbUpdateConcurrencyException gives us the ability to reload this entity from the database.
foreach (var entry in staleValues)
{
if (entry.Entity is SystemData)
{
await entry.ReloadAsync();
}
}
// Now that we have the latest value loaded, we'll try calling this method again.
return(await ComputePrns(numberOfPrnsNeeded));
}
else
{
// Something else bad happened and it's not possible to fix that here.
exceptionDispatchInfo.Throw();
throw new Exception("This will never be thrown.");
}
}