I have got an StringHashTable class from
http://preshing.com/20110603/hash-table-performance-tests/
The following are parts of source :
class StringHashTable
{
static uint fnv1Hash(const char *key)
{
unsigned int hash = 2166136261ul;
for (const char *s = key; *s; s++)
hash = (16777619 * hash) ^ (*s);
return hash;
};
uint &operator[](const char *key)
{
uint hash = fnv1Hash(key) & (m_tableSize - 1);
Bucket *firstBucket = m_table + hash;
Bucket *b = firstBucket;
if (b->key)
{
do
{
if (strcmp(b->key, key) == 0)
return b->value;// Found existing bucket
b = b->next;
} while (b);
}
..........
}
}
Suppose that I have the global var :
StringHashTable hashtable(1024) ; //m_tableSize now 1024
And then the following is in main :
hashtable["0000"] = 0 ;
....
hashtable["9999"] = 9999 ;
After fill in all the data I need , thread 1 to n will get value according to key
while(1)
{
s = get(); //return string like "0000" ... "9999"
echo << hashtable[s.c_str()] << endl ;
}
I wonder if the StringHashTable would work fine in thread at first ,
because the function fnv1Hash is static , on second thought , there is no
static member data in this StringHashTable , so while thread1 is doing
hashtable["0000"] and thread2 is doing hashtable["9999"] at the very same time
both thread1 are calling fnv1Hash they will both get the right hash returned !!!
My question is : different thread call static uint fnv1Hash(const char *key) with
different key at the very same time still work fine ? In StringHashTable , fnv1Hash
is static for any reason ?!
The function fnv1Hash() doesn't access any non-local state other than the data pointed to by key. Assuming the content of the array key points to isn't written to concurrently, there is no threading issue. Of course, if another thread writes to the array pointed to by key, all bets are off.
Given that fnv1Hash() does access any of the object's data it doesn't need a this pointer. Thus, it is made static to indicate both to the human reader and the compiler that the objects won't be accessed implicitly. For the compiler the upshot is that it doesn't need to pass a this pointer.
Related
I have multiple types of classes.
Each type has an array and an index in the array.
If an outside function knows only a string ID of a class and wants to use it's public function,
it must search for that particular class by ID in it's array.
This is really inefficient.
All my classes created at runtime and a function which creates it, puts it into an array.
I want to create a lookup table of some sort for this when the classes are created, so any outside
function if wants to use one class it does not have to for loop on the class's array and check each ID if it matches but to be able to reach the class by some struct or array.
Here how it is done now:
#define MAX_ONE_TYPES 20
int createdOneTypesCounter = 0;
// Create one type of classes in one for loop and put it into an array.
// We must keep track of the index because a class can be created later
// at runtime so we must keep increasing the index. I don't check for max index now...
// oneTypes is a JSON OBJECT
for (JsonPair oneTypeRef: oneTypes) {
const char* oneTypeID = oneTypeRef.key().c_str();
JsonObject oneTypeOptions = oneTypes[oneTypeID];
oneTypeClasses[createdOneTypesCounter ] = new oneTypeClass(oneTypeOptions);
createdOneTypesCounter++;
}
class oneTypeClass{
private:
// using an external ram for this kinda stuffs.
const size_t IDS_AND_NAMES_SIZE = 500;
const char * id = (char *) ps_malloc (IDS_AND_NAMES_SIZE * sizeof (char));
public:
thermHandler(JsonObject options){
// She got an ID on creation.
id = strdup(options["id"]);
}
void setModes(boolean mode){
// set some mode...
}
boolean isMyID(const char* packetID){
if( strcmp(id, packetID) == 0 ){return true;}
return false;
}
};
oneTypeClass* oneTypeClasses[MAX_ONE_TYPES] EXT_RAM_ATTR;
// Here comes an outside function. Wants to set a boolean in a class with specific ID.
static const inline void setOneTypeMode(JsonObject packet){
for(int i = 0; i < MAX_ONE_TYPES; i++){
if(oneTypeClasses[i] != NULL && oneTypeClasses[i]->isMyID(packet["id"])){
oneTypeClasses[i]->setModes(packet["mode"]);
break;
}
}
}
And here is my problem. I must search for a class by ID every time some outside function wants to do something with one of the classes.
I don't know how would i do it.
In JS i would create an object for a lookup table and every time a class is created i would put it's ID for the key and it's index to the value like this:
var oneTypeClass_Lookup{
"CLASS ID STRING" : "CLASS INDEX IN ARRAY"
};
//And a function would do it like this:
static const inline void setOneTypeMode(JsonObject packet){
int myClassIndex = oneTypeClass_Lookup[ packet["id"] ];
oneTypeClasses[myClassIndex]->setModes(packet["mode"]);
}
I'm doing this for "mass operation":
static const inline int getOneTypeClassIndex(const char* packetID){
for(int i = 0; i < MAX_THERMS; i++){
if(oneTypeClasses[i] != NULL && oneTypeClasses[i]->isMyID(packetID)){
return i;
}
}
return -1;
}
static const inline void setThing(int newThing, const char* packetID){
int index = getOneTypeClassIndex(packetID);
if( index > -1 ){
oneTypeClasses[index]->setNewThing(newThing);
}
}
static const inline void setThing_Two(int newThing, const char* packetID){
int index = getOneTypeClassIndex(packetID);
if( index > -1 ){
oneTypeClasses[index]->setNewThing(newThing);
}
}
But i can't do this in C or Arduino C++. I hope i was clear.
UI: Class id consist of numbers and characrers. The id can never start with a number. Example: "v_kw62ffss_xg0syjlvrokbxciv65a8y"
Iam new to using Core Foundations. I want to use dictionary to store some key value pair. The value must be a pointer to a struct. This pointer is pointing to dynamically allocated buffer.
CFMutableDictionaryRef init_hash_table() {
return CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
}
This is used to create the dictionary and the return value is stored as global variable.
CFNumberRef
create_hash_key(int sd) {
return CFNumberCreate(NULL, kCFNumberIntType, &sd);
}
int
add_hash_entry(CFMutableDictionaryRef dict, int sd, void *pkt) {
CFNumberRef key = create_hash_key(sd);
CFDictionarySetValue(dict, key, pkt);
return 0;
}
When I execute this code, I get segfault. I see that pkt has a valid address and key seems to be created. Does anyone know how to assign a pointer to value part?
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000011
0x00007fff8c9f339f in objc_msgSend_fixup ()
Any ideas?
The problem is the kCFTypeDictionaryValueCallBacks argument. From the documentation:
kCFTypeDictionaryValueCallBacks
Predefined CFDictionaryValueCallBacks structure containing a set of
callbacks appropriate for use when the values in a CFDictionary are
all CFType-derived objects.
So in your case, CFRetain() is called on the pointer when the value is added to the
dictionary. This causes the crash because the pointer does not point to a CoreFoundation
object.
You can create the dictionary with
CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, NULL);
instead, so that no "reference counting" will be done on the value.
Alternatively, you can wrap the pointer into a CFDataRef and put that into the
dictionary.
In both cases it is your responsibility that the pointer is still valid
when the value is retrieved from the dictionary later.
Here is a simple example how you could implement refcounting for your custom objects:
typedef struct {
int refcount;
int val;
} mystruct;
const void *myretain(CFAllocatorRef allocator, const void *value)
{
mystruct *p = (mystruct *)value;
p->refcount++;
return p;
}
void myrelease(CFAllocatorRef allocator, const void *value)
{
mystruct *p = (mystruct *)value;
if (p->refcount == 1)
free(p);
else
p->refcount--;
}
int main(int argc, const char * argv[])
{
mystruct *p = malloc(sizeof(*p));
p->refcount = 1;
p->val = 13;
CFDictionaryValueCallBacks vcb = { 0 , myretain, myrelease, NULL, NULL };
CFMutableDictionaryRef dict = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &vcb);
int sd = 13;
CFNumberRef key = CFNumberCreate(NULL, kCFNumberIntType, &sd);
CFDictionarySetValue(dict, key, p);
// refcount == 2
myrelease(NULL, p);
// refcount == 1
mystruct *q = CFDictionaryGetValue(dict, key);
// refcount is still 1, "GetValue" does not increment the refcount
CFRelease(dict);
// object is deallocated
return 0;
}
Platform : Windows 7
I'm developing a project for known text cipher attack in which;
Main process creates n child processes
Child processes decrypt an encrypted string, key subspace is partitioned according to number of child processes
Communication between child processes are by a static variable
for(int i = 0; i<info.totalNumberOfChildren; i++)
{
startChild( &info.childInfoList[i]);
//_beginthread(startChild, 0, &info.childInfoList[i]);
}
Above code works fine since:
First child starts execution, the key is set as a number such as 8 for testing purposes which is within the first child's partition, so first child finds the key, reports and sets true the killSwitch.
All the other children that are created are closed even before checking the first key as the killSwitch is true.
When I however do this :
for(int i = 0; i<info.totalNumberOfChildren; i++)
{
//startChild( &info.childInfoList[i]);
_beginthread(startChild, 0, &info.childInfoList[i]);
}
I get an access violation error. What could possibly be my source of error ?
Edit: I will try to share as relevant code as I can
startChild does the following:
void startChild( void* pParams)
{
ChildInfo *ci = (ChildInfo*)pParams;
// cout<<"buraya geldi"<<endl;
ChildProcess cp(*ci);
// write to log
cp.completeNextJob();
}
childInfo holds the following :
// header file
class ChildInfo
{
public:
ChildInfo();
ChildInfo(char * encrypted, char * original, static bool killSwitch, int totalNumOfChildren, int idNum, int orjLen);
void getNextJob();
bool keyIsFound();
Des des;
void printTest();
bool stopExecution;
bool allIsChecked;
char * encyptedString;
char * originalString;
int id;
int orjStrLen;
private:
int lastJobCompleted;
int totalNumberOfChildren;
int jobDistBits;
};
completeNextJob() does the following :
void ChildProcess::completeNextJob()
{
cout<<"Child Id : "<<info.id<<endl;
// cout<<"Trying : "<<info.encyptedString<<endl; // here I got an error
char * newtrial = info.encyptedString;
char * cand = info.des.Decrypt(newtrial); // here I also get an error if I comment out
/*
cout<<"Resultant : "<<cand<<endl;
cout<<"Comparing with : "<<info.originalString<<endl;
*/
bool match = true;
for(int i = 0; i<info.orjStrLen; i++)
{
if(!(cand[i] == info.originalString[i]))
match = false;
}
if(match)
{
cout<<"It has been acknowledged "<<endl;
info.stopExecution = true;
return;
}
else
{
if(!info.keyIsFound())
{
if(!info.allIsChecked)
{
info.getNextJob();
completeNextJob();
}
else
{
}
}
else
{
}
}
}
decrypt() method does the following :
char * Des::Decrypt(char *Text1)
{
int i,a1,j,nB,m,iB,k,K,B[8],n,t,d,round;
char *Text=new char[1000];
unsigned char ch;
strcpy(Text,Text1); // this is where I get the error
i=strlen(Text);
keygen();
int mc=0;
for(iB=0,nB=0,m=0;m<(strlen(Text)/8);m++) //Repeat for TextLenth/8 times.
{
for(iB=0,i=0;i<8;i++,nB++)
{
ch=Text[nB];
n=(int)ch;//(int)Text[nB];
for(K=7;n>=1;K--)
{
B[K]=n%2; //Converting 8-Bytes to 64-bit Binary Format
n/=2;
} for(;K>=0;K--) B[K]=0;
for(K=0;K<8;K++,iB++) total[iB]=B[K]; //Now `total' contains the 64-Bit binary format of 8-Bytes
}
IP(); //Performing initial permutation on `total[64]'
for(i=0;i<64;i++) total[i]=ip[i]; //Store values of ip[64] into total[64]
for(i=0;i<32;i++) left[i]=total[i]; // +--> left[32]
// total[64]--|
for(;i<64;i++) right[i-32]=total[i];// +--> right[32]
for(round=1;round<=16;round++)
{
Expansion(); //Performing expansion on `right[32]' to get `expansion[48]'
xor_oneD(round);
substitution();//Perform substitution on xor1[48] to get sub[32]
permutation(); //Performing Permutation on sub[32] to get p[32]
xor_two(); //Performing XOR operation on left[32],p[32] to get xor2[32]
for(i=0;i<32;i++) left[i]=right[i]; //Dumping right[32] into left[32]
for(i=0;i<32;i++) right[i]=xor2[i]; //Dumping xor2[32] into right[32]
} //rounds end here
for(i=0;i<32;i++) temp[i]=right[i]; // Dumping -->[ swap32bit ]
for(;i<64;i++) temp[i]=left[i-32]; // left[32],right[32] into temp[64]
inverse(); //Inversing the bits of temp[64] to get inv[8][8]
/* Obtaining the Cypher-Text into final[1000]*/
k=128; d=0;
for(i=0;i<8;i++)
{
for(j=0;j<8;j++)
{
d=d+inv[i][j]*k;
k=k/2;
}
final[mc++]=(char)d;
k=128; d=0;
}
} //for loop ends here
final[mc]='\0';
char *final1=new char[1000];
for(i=0,j=strlen(Text);i<strlen(Text);i++,j++)
final1[i]=final[j]; final1[i]='\0';
return(final);
}
Windows is trying to tell you why your program crashed. Please use a debugger to see what Windows is talking about. Location X is important: it should tell you whether your program is dereferencing NULL, overflowing a buffer, or doing something else. The call stack at the time of the crash is also very important.
Debugger is your best friend, try to use it and check step by step what could cause this access violation.
I think that info.encyptedString is not initialized correctly and pointing to not allocated memory, but I cant be sure because you didn't show this part of code.
And of course you must protect your shared resources (info) using some synchronization objects like critical section or mutex or semaphore.
I don't know, the basic issue seems pretty straightforward to me. You have multiple threads executing simultaneously, which access the same information via *pParams, which presumably is of type ChildInfo since that's what you cast it to. That info must be getting accessed elsewhere in the program, perhaps in the main thread. This is corrupting something, which may or may not have to do with Text1 or info.id, these errors can often be 'non-local' and hard to debug for this reason. So start mutex-protecting the entire thread (within your initial loop), and then zero in on the critical sections by trial and error, i.e. mutex-protect as small a region of code as you can get away with without producing errors.
I have working on multithreaded application I am passing IMAGETHREADINFO structure in thread here nSock is showing garbage value. What is the problem here.pointer to IMAGETHREADINFO is declared as member variable of CServerConnectionMgr class.
typedef struct
{
int nScok;
CServerConnectionMgr* pConMgr;
}IMAGETHREADINFO;
void StartImageThread(SOCKET nSock)
{
stThreadInfo = new IMAGETHREADINFO;
stThreadInfo.pConMgr = this;
stThreadInfo.nScok = nSock;
m_hRecordImageThread = CreateThread ( NULL,0, (LPTHREAD_START_ROUTINE)StreamImageThread,(void*)&stThreadInfo, 0,&m_nRecordImageThreadID);
if ( NULL == m_hRecordImageThread)
{
return;
}
int CServerConnectionMgr::StreamImageThread(void *args)
{
IMAGETHREADINFO *pImageThreadInfo = (IMAGETHREADINFO*)&args;
}
This is variable pImageThreadInfo->nSock showing some garbage value
This pImageThreadInfo->pConMgr is coming correctly
I this is showing wrong value
(void*)&stThreadInfo is a pointer to the stThreadInfo pointer. You likely want to remove the &
And then, also change IMAGETHREADINFO *pImageThreadInfo = (IMAGETHREADINFO*)&args;, remove the &
I have a situation in Visual C++ 2008 that I have not seen before. I have a class with 4 STL objects (list and vector to be precise) and integers.
It has a method:
inline int id() { return m_id; }
The return value from this method is corrupt, and I have no idea why.
debugger screenshot http://img687.imageshack.us/img687/6728/returnvalue.png
I'd like to believe its a stack smash, but as far as I know, I have no buffer over-runs or allocation issues.
Some more observations
Here's something that puts me off. The debugger prints right values in the place mentioned // wrong ID.
m_header = new DnsHeader();
assert(_CrtCheckMemory());
if (m_header->init(bytes, size))
{
eprintf("0The header ID is %d\n", m_header->id()); // wrong ID!!!
inside m_header->init()
m_qdcount = ntohs(h->qdcount);
m_ancount = ntohs(h->ancount);
m_nscount = ntohs(h->nscount);
m_arcount = ntohs(h->arcount);
eprintf("The details are %d,%d,%d,%d\n", m_qdcount, m_ancount, m_nscount, m_arcount);
// copy the flags
// this doesn't work with a bitfield struct :(
// memcpy(&m_flags, bytes + 2, sizeof(m_flags));
//unpack_flags(bytes + 2); //TODO
m_init = true;
}
eprintf("Assigning an id of %d\n", m_id); // Correct ID.
return
m_header->id() is an inline function in the header file
inline int id() { return m_id; }
I don't really know how best to post the code snippets I have , but here's my best shot at it. Please do let me know if they are insufficient:
Class DnsHeader has an object m_header inside DnsPacket.
Main body:
DnsPacket *p ;
p = new DnsPacket(r);
assert (_CrtCheckMemory());
p->add_bytes(buf, r); // add bytes to a vector m_bytes inside DnsPacket
if (p->parse())
{
read_packet(sin, *p);
}
p->parse:
size_t size = m_bytes.size(); // m_bytes is a vector
unsigned char *bytes = new u_char[m_bytes.size()];
copy(m_bytes.begin(), m_bytes.end(), bytes);
m_header = new DnsHeader();
eprintf("m_header allocated at %x\n", m_header);
assert(_CrtCheckMemory());
if (m_header->init(bytes, size)) // just set the ID and a bunch of other ints here.
{
size_t pos = DnsHeader::SIZE; // const int
if (pos != size)
; // XXX perhaps generate a warning about extraneous data?
if (ok)
m_parsed = true;
}
else
{
m_parsed = false;
}
if (!ok) {
m_parsed = false;
}
return m_parsed;
}
read_packet:
DnsHeader& h = p.header();
eprintf("The header ID is %d\n", h.id()); // ID is wrong here
...
DnsHeader constructor:
m_id = -1;
m_qdcount = m_ancount = m_nscount = m_arcount = 0;
memset(&m_flags, 0, sizeof(m_flags)); // m_flags is a struct
m_flags.rd = 1;
p.header():
return *m_header;
m_header->init: (u_char* bytes, int size)
header_fmt *h = (header_fmt *)bytes;
m_id = ntohs(h->id);
eprintf("Assigning an id of %d/%d\n", ntohs(h->id), m_id); // ID is correct here
m_qdcount = ntohs(h->qdcount);
m_ancount = ntohs(h->ancount);
m_nscount = ntohs(h->nscount);
m_arcount = ntohs(h->arcount);
You seem to be using a pointer to an invalid class somehow. The return value shown is the value that VS usually uses to initialize memory with:
2^32 - 842150451 = 0xCDCDCDCD
You probably have not initialized the class that this function is a member of.
Without seeing more of the code in context.. it might be that the m_id is out of the scope you expect it to be in.
Reinstalled VC++. That fixed everything.
Thank you for your time and support everybody! :) Appreciate it!