Unfortunately, I forgot to record the time that I took the heap dump. I hope that somewhere in the heap, the standard library caches something like System.currentTimeMillis(). Unfortunately, I do not have any business objects that cache it.
One difficult option I have it to browse all the threads, and see if their local variables stored a timestamp somewhere. However, this is not technique I can apply to all heap dumps.
I looked at java.lang.System in openJDK and it doesn't look like we cache a value. We go to native code to get the current time, but we don't store the result from native code anywhere. https://hg.openjdk.java.net/jdk8/jdk8/jdk/file/4d891c8db5c1/src/share/classes/java/lang/System.java
The heap dump file contains a timestamp right in its header. But there is a zero-terminated string at the beginning, which would make the exact position of the timestamp dynamic, if the string wouldn’t be always the same.
So for a short, ad-hoc lookup in your actual files, you might simply assume the usual position and extract the timestamp as
try(RandomAccessFile raf = new RandomAccessFile(hprofFileLocation, "r")) {
raf.seek(23);
System.out.println(hprofFileLocation+" created "+Instant.ofEpochMilli(raf.readLong()));
}
whereas a clean solution would read the zero terminated string, skip the subsequent int value and read the timestamp from the resulting position, e.g.
try(FileChannel fch = FileChannel.open(
Paths.get(hprofFileLocation), StandardOpenOption.READ)) {
ByteBuffer bb = fch.map(
FileChannel.MapMode.READ_ONLY, 0, Math.min(Integer.MAX_VALUE, fch.size()));
do {} while(bb.get() != 0); // zero terminate string, usually "JAVA PROFILE 1.0.[12]"
int pointerSize = bb.getInt();
long timeStamp = bb.getLong();
System.out.println(hprofFileLocation+" created "+Instant.ofEpochMilli(timeStamp));
}
Related
I want to insert documents into Couchbase as a bulk in Java. So what is the standard procedure for Generating keys for each document in java..?
You could use a Couchbase "counter" document as a form of sequence. Using the reactive approach with the Java SDK, this would go something like this, assuming your batch is a List<JsonObject> with each content to save to Couchbase:
//start with a sequence of contents to save
Observable.from(listOfDocumentContent)
//for each content, asynchronously generate something...
.flatMap(content -> bucket.async() //assuming bucket is a `Bucket`
//atomically generate an increasing value, starting from 0
.counter("DOCUMENT_KEY_GENERATOR", 1, 0) //use a more relevant document key
//this gives a `JsonLongDocument`, so extract the number and turn that + the original content into a `JsonDocument` to be saved
.map(cDoc -> JsonDocument.create(KEY_PREFIX + cDoc.content(), content))
)
//next up, asynchronously saving each document we generated in the previous step... You could also use insert since you don't expect the keys to already exist in Couchbase
.flatMap(docToSave -> bucket.async().upsert(docToSave))
//this will perform the above asynchronously but wait for the last doc in the batch to finish saving:
.toBlocking().last();
Notice we use a KEY_PREFIX when generating the document to be saved, so that there is less risk of collision (otherwise, other documents in the bucket could be named "1" if you do that for multiple types of documents inside the same bucket).
Also tune the saving method used to your needs (here upsert vs create vs update, TTL, durability requirements, etc...)
This seemed like it should be very simple to do yet I've not been able to find an answer after weeks of looking.
I'm trying to remove strings that are no longer needed. Regex_replace sounds perfect but is not available in MySQL.
In MySQL how would I accomplish changing this:
[quote=ABC;xxxxxx]
to this:
[quote=ABC]
The issues are:
- this can appear anywhere in a text blob
- the xxxxxx can only be numeric but may be 6, 7 or 8 characters long
- not adding/removing any rows, just rewriting the contents of one column on one row at a time.
Thanks.
I don't think you really need REGEX_Replace (though it would make things easier of course).
Assuming that the example you presented is a real reflection of what you have:
Your starting point is with the string [quote=<something>;, meaning that you can start searching for [quote=,
Once you found it, you need to search for ; and after that for ],
Once you found them both, you know what to extract when where to start for the next search (if the pattern you mentioned can appear more than once within a singe blob.
Did I get you correctly?
EDIT
This paradigm is aimed to convert all instances of [quote=ABC;xxxxxx] to [quote=ABC] under the following assumptions:
The pattern can appear any number of times within the input string,
The length of xxxxxx is not fixed,
The resulting string (after removing all the appearances of ;xxxxxx) should replace the value in the table,
Performance is not an issue since either this is going to be a one-time job (through the whole table) or it will run every time on a single string (e.g. before INSERTing a new record).
Some MySQL functions that will be used:
INSTR: Searches within a string for the first appearance of a sub-string and returns the position (offset) where the sub-string was found,
SUBSTR: Returns a substring from a string (several ways to use it),
CONCAT: Concatenates two or more strings.
The guidelines presented here apply for the manipulation of a single INPUT string. If this needs to be used over, say, a whole table, simply get the strings into a CURSOR and loop.
Here are the steps:
Declare five INT local variables to serve as indices and total input string length, say L_Start, L_UpTo, l_Total_Length, l_temp1 and l_temp 2, setting the initial value for l_Start = 1 and l_Total_Length = LENGTH(INPUT_String),
Declare a string variable into which you will copy the "cleaned" result and initiate it as '', say l_Output_str; also declare a temporary string to hold the value of 'ABD', say l_Quote,
Start a infinite loop (you will set the exit condition within it; see below),
Exit loop if l_Start >= l_Total_Length (here is one of the two exit points from the loop),
Find the first location of '[quote=' within the input string starting from L_Start,
If the returned value is 0 (i.e. substring not found), concatenate the current contents of l_Output_str with whatever remains if the input string from position L_start (e.g. SET l_Output_str = CONCAT(l_Output_str,SUBSTR(INPUT_String,L_Start) ;) and exit loop (second exit position),
Search the input string for the ; symbol starting from L_start + 7 (i.e. the length of [quote=) and save the value in l_temp_1,
Search the input string for the ] symbol starting from L_start + 7 + l_temp2 and save the value in l_temp_2,
Add the found result to output string as SET l_Output_str = CONCAT(l_Output_str,'[quote=',SUBSTR(INPUT_String,L_Start + 7, l_temp_2 - l_temp_1),']') ;,
Set L_Start = L_Start + 7 + l_temp_2 + 1 ;
End of loop.
Notes:
As I neither made the code nor tested it, it is possible that I'm not setting indices correctly; you will need to perform detailed tests to make get it working as needed;
The above IS the method I suggested;
If the input string is very long (many MBs), you might observe poor performance (i.e. it might take few seconds to complete) because of the concatenations. There are some steps that can be taken to improve performance, but let's have this working first and then, if needed, tackle the performance issues.
Hope that the above is clear and comprehensive.
The Reference Source page for stringbuilder.cs has this comment in the ToString method:
if (chunk.m_ChunkLength > 0)
{
// Copy these into local variables so that they
// are stable even in the presence of ----s (hackers might do this)
char[] sourceArray = chunk.m_ChunkChars;
int chunkOffset = chunk.m_ChunkOffset;
int chunkLength = chunk.m_ChunkLength;
What does this mean? Is ----s something a malicious user might insert into a string to be formatted?
The source code for the published Reference Source is pushed through a filter that removes objectionable content from the source. Verboten words are one, Microsoft programmers use profanity in their comments. So are the names of devs, Microsoft wants to hide their identity. Such a word or name is substituted by dashes.
In this case you can tell what used to be there from the CoreCLR, the open-sourced version of the .NET Framework. It is a verboten word:
// Copy these into local variables so that they are stable even in the presence of race conditions
Which was hand-edited from the original that you looked at before being submitted to Github, Microsoft also doesn't want to accuse their customers of being hackers, it originally said races, thus turning into ----s :)
In the CoreCLR repository you have a fuller quote:
Copy these into local variables so that they are stable even in the presence of race conditions
Github
Basically: it's a threading consideration.
In addition to the great answer by #Jeroen, this is more than just a threading consideration. It's to prevent someone from intentionally creating a race condition and causing a buffer overflow in that manner. Later in the code, the length of that local variable is checked. If the code were to check the length of the accessible variable instead, it could have changed on a different thread between the time length was checked and wstrcpy was called:
// Check that we will not overrun our boundaries.
if ((uint)(chunkLength + chunkOffset) <= ret.Length && (uint)chunkLength <= (uint)sourceArray.Length)
{
///
/// imagine that another thread has changed the chunk.m_ChunkChars array here!
/// we're now in big trouble, our attempt to prevent a buffer overflow has been thawrted!
/// oh wait, we're ok, because we're using a local variable that the other thread can't access anyway.
fixed (char* sourcePtr = sourceArray)
string.wstrcpy(destinationPtr + chunkOffset, sourcePtr, chunkLength);
}
else
{
throw new ArgumentOutOfRangeException("chunkLength", Environment.GetResourceString("ArgumentOutOfRange_Index"));
}
}
chunk = chunk.m_ChunkPrevious;
} while (chunk != null);
Really interesting question though.
Don't think that this is the case - the code in question copies to local variables to prevent bad things happening if the string builder instance is mutated on another thread.
I think the ---- may relate to a four letter swear word...
I am using the following code to read an error message from a byte array and it works fine the first time but if I try to access it the second time it throws an error:
errorData = process.standardError.readUTFBytes(process.standardError.bytesAvailable);
StandardError is of type InboundPipe?
The error is:
Error: Error #3212: Cannot perform operation on a NativeProcess that is not running.
even though the process is running (process.running is true). It's on the second call to readUTFBytes that seems to be the cause.
Update:
Here is the code calling the same call one after another. The error happens on the next line and process.running has not changed from true. Happens on the second call.
errorData = process.standardError.readUTFBytes(process.standardError.bytesAvailable);
errorData = process.standardError.readUTFBytes(process.standardError.bytesAvailable);
I also found out the standardError is a InboundPipe instance and implements IDataInput.
Update 2:
Thanks for all the help. I found this documentation when viewing the bytesAvailable property.
[Read Only] Returns the number of bytes of data available for reading
in the input buffer. User code must call bytesAvailable to ensure that
sufficient data is available before trying to read it with one of the
read methods.
When I call readUTFBytes() it resets the bytes available to 0. So when I read it a second time and there are no bytes available it causes the error. The error is or may be incorrect in my opinion or the native process.running flag is incorrect.
I looked into seeing if it has a position property and it does not, at least not in this instance.
Could you try to set position to zero before reading process, especially before repetitive access:
Moves, or returns the current position, in bytes, of the file pointer into the ByteArray object. This is the point at which the next call to a read method starts reading or a write method starts writing.
//ByteArray example
var source: String = "Some data";
var data: ByteArray = new ByteArray();
data.writeUTFBytes(source);
data.position = 0;
trace(data.readUTFBytes(data.bytesAvailable));
data.position = 0;
trace(data.readUTFBytes(data.bytesAvailable));
This was a tricky problem since the object was not a byte array although it looks and acts like one (same methods and almost same properties). It is an InboundPipe that also implements IDataInput.
I found this documentation when viewing the bytesAvailable property.
[Read Only] Returns the number of bytes of data available for reading
in the input buffer. User code must call bytesAvailable to ensure that
sufficient data is available before trying to read it with one of the
read methods.
When I call readUTFBytes() it resets the bytes available to 0. So when I call it a second time and there are no bytes available it causes the error. The error is or may be incorrect in my opinion or the native process.running flag is incorrect although I have reason to believe it's the former.
The solution is to check bytesAvailable before calling read operations and store the value if it needs to be accessed later.
if (process.standardError.bytesAvailable) {
errorData = process.standardError.readUTFBytes(process.standardError.bytesAvailable);
errorDataArray.push(errorData);
}
I looked into seeing if it has a position property and it does not, at least not in this instance.
I am totally new to cocos2d-x ios game development and really learning a lot from stackoverflow.Just want to thank all the software coders.Now my question is I am making a game with levels and high score.But still couldn't find a way to store the high score and the levels cleared.When the game restarts all the values are set to initial values as there is no database to fetch.I have heard about userdefault in cocos2d-x but really couldn't find a way to execute. Can anyone help me with a sample. I will be thankful to you
CCUserDefault acts as a key value pair and stores a value corresponding to the keys.Suppose you want to store a high score of your game so that when the user restarts the game after exiting,the changes should persist
For this,in your .cpp file take a const key value at the top after header inclusion
const char *HIGH_SCORE="key1";
key1 is a key and this key must be different for every const char * which you declare
Delete the lines in init function after these lines upto return true statement.
if(!CCLayer::init())
{
return false;
}
Don’t delete return true.Then in your init function write the following code
CCUserDefault *def=CCUserDefault::sharedUserDefault();
def->setIntegerForKey(HIGH_SCORE, 2000);
def->flush();
Here def is a pointer to CCUserDefault and it will help to access all the methods in that class.
SetIntegerForKey is the method which sets the corresponding integer value to the constant char *.
There are many more functions to store string, float, bool and double values.
def->flush() is a function which flushes the contents to the xml file. It basically saves the data to the xml file
To retrieve values from the key,suppose we want to retrieve the high score and display on a label
int high_score=def->getIntegerForKey(HIGH_SCORE);
Here we are converting the integer into a string so that we can display on a label
char s[4];
sprintf(s,"%d", high);
Adding the score to a label
CCLabelTTF *high_label=CCLabelTTF::create(s, "Arial.fnt", 20);
high_label->setPosition(ccp(200,200));
this->addChild(high_label);
Now run your project and you will see 2000 on the screen
Now stop the run and comment the following lines
//def->setIntegerForKey(HIGH_SCORE, 2000);
//def->flush();
Again re run the project and still the value is 2000 on the screen.It means that now HIGH_SCORE is stored in the xml file and the value is retrieved from it.Therefore the changes persist even after application is closed
If you want to store basic information like High Score, Current Level etc then you can use CCUserDefault and if you want to store complex data then either you can use SQLite or CCDictionary
Here is pseudo code to store and retrieve High Score in Cocos2dx-3.0:
const char* KEY_HIGH_SCORE = "high_score";
// Store High Score
UserDefault::getInstance()->setIntegerForKey(KEY_HIGH_SCORE, 100);
// Retrieve High Score.
int high_score = UserDefault::getInstance()->getIntegerForKey(KEY_HIGH_SCORE);