In pure C code in different projects that involve Postgresql server programming which I'm working with now, I keep encountering the function "IsA()" which returns a boolean and checks whether or not 2 instances of a struct belong to the same struct. I suppose.
One of them:
https://github.com/guotao0628/pipelinedb/blob/master/src/backend/executor/nodeBitmapAnd.c#L123
for (i = 0; i < nplans; i++)
{
PlanState *subnode = bitmapplans[i];
TIDBitmap *subresult;
subresult = (TIDBitmap *) MultiExecProcNode(subnode);
if (!subresult || !IsA(subresult, TIDBitmap)) /*what's IsA(...) ? */
elog(ERROR, "unrecognized result from subplan");
if (result == NULL)
result = subresult; /* first subplan */
I need to port some of that C code to other strictly typed language. Hence, I need to know how "isA()" is implemented under the hood. But I haven't found it anywhere. Supposedly it's defined in some library.
Where can I find its definition?
IsA is a macro which is defined in this header file in Postgresql source code.
Related
I have initialised 3 instances of a cache I have defined using typedef. I have done some processing on them in a serious of if statements in the following way :
cache cache1;
cache cache2;
cache cache3;
int a;
void main(...) {
if (a == 0) {
cache1.attribute = 5;
}
else if (a == 1) {
cache2.attribute = 1;
}
else if (a == 2) {
cache3.attribute = 2 ;
}
However now I need to make the design modular in the following way:
cache cache1;
cache cache2;
cache cache3;
void cache_operator( cache user_cache, int a ) {
user_cache.attribute = a;
}
void main(...) {
if (a == 0) {
cache_operator(cache1,5);
}
else if (a == 1) {
cache_operator(cache2,1);
}
...
I am having trouble with passing the cache to the method. I'm used to java programming and I'm not very familiar with c pointers. However, if I pass the cache itself as shown above I am passing a copy of the cache on the stack which then produces results different to the original code. How do I properly transform the first design into the second design when it comes to passing the appropriate cache to the function and making sure it is accessed properly.
In C language, if you want to keep track of the original 'data' instead of creating a copy in the function, you have to pass the pointer of that data to that function.
Pointer in C is just like the reference to object in JAVA.
Following is how you do it.
void cache_operator( cache *user_cache, int a )
{
user_cache->attribute = a;
}
Following is how you call the function.
cache_operator(&cache1,5);
I also started with JAVA. I don't know why some universities nowadays use JAVA as beginning language... It is quite strange, since JAVA is a high-level language making the abstraction of low-level detail, whereas C is a rather low-level language. In the past, this will never be the case..
I'm currently trying to make an application using the nrf51 development kit & I'm trying to use the timer driver, when I induled the C & H files of the driver I got some error :
static const nrf_drv_timer_config_t m_default_config[] = {// here it told me there is error #1
#if (TIMER0_ENABLED == 1)
NRF_DRV_TIMER_DEFAULT_CONFIG(0),
#endif
#if (TIMER1_ENABLED == 1)
NRF_DRV_TIMER_DEFAULT_CONFIG(1),
#endif
#if (TIMER2_ENABLED == 1)
NRF_DRV_TIMER_DEFAULT_CONFIG(2)
#endif
};
// here it told me there is error #2
ret_code_t nrf_drv_timer_init(nrf_drv_timer_t const * const p_instance,
nrf_drv_timer_config_t const * p_config,
nrf_timer_event_handler_t timer_event_handler)
{
ASSERT((p_instance->instance_id) < TIMER_INSTANCE_NUMBER);
ASSERT(TIMER_IS_BIT_WIDTH_VALID(p_instance->instance_id, p_config->bit_width));
if (m_cb[p_instance->instance_id].state != NRF_DRV_STATE_UNINITIALIZED)
{
return NRF_ERROR_INVALID_STATE; // timer already initialized
}
if (p_config == NULL)
{
p_config = &m_default_config[p_instance->instance_id];
}
#ifdef SOFTDEVICE_PRESENT
if (p_instance->p_reg == NRF_TIMER0)
{
return NRF_ERROR_INVALID_PARAM;
}
#endif
nrf_drv_common_irq_enable(p_instance->irq, p_config->interrupt_priority);
mp_contexts[p_instance->instance_id] = p_config->p_context;
if (timer_event_handler != NULL)
{
m_timer_event_handlers[p_instance->instance_id] = timer_event_handler;
}
else
{
return NRF_ERROR_INVALID_PARAM;
}
nrf_timer_mode_set(p_instance->p_reg, p_config->mode);
nrf_timer_bit_width_set(p_instance->p_reg, p_config->bit_width);
nrf_timer_frequency_set(p_instance->p_reg, p_config->frequency);
m_cb[p_instance->instance_id].state = NRF_DRV_STATE_INITIALIZED;
return NRF_SUCCESS;
}
the error #1 says that "an empty initializer is invalid for an array with unspecified bound"
the error #2 says that it expected an expression
I till now didn't use any of these functions in the main.c code, I'm just added the header files that will be used further.
Error 1: Apparently neither of TIMERx_ENABLED is 1, so the array will be empty. As it is const, there is no chance to initialize it later. That would also result in an array of zero elements, which is not allowed. Easiest might be to have an #else clause with a single null entry. However, I suspect you have to configure the stuff for your system first. Read the documentation.
Error 2: might be a follow up error, or one of the custom types are not defined - hard to say without more info, or the location the error is reported is simply not that of the actual error, or ... . Best is to fix the first error, then try again for error 2.
If you are using examples from nordic then the defines are either in nrf_drv_config.h or in the sdk_config.h for new versions of the nordic sdk.
You have to enable the timers by changing the TIMER_ENABLED define to 1. Then do the same for the timers you want to use.
You could make these defines yourself as other people have suggested.
I am reading a file say x.c and I have to find for the string "shared". Once the string like that has been found, the following has to be done.
Example:
shared(x,n)
Output has to be
*var = &x;
*var1 = &n;
Pointers can be of any name. Output has to be written to a different file. How to do this?
I'm developing a source to source compiler for concurrent platforms using lex and yacc. This can be a routine written in C or if u can using lex and yacc. Can anyone please help?
Thanks.
If, as you state, the arguments can only be variables and not any kind of other expressions, then there are a couple of simple solutions.
One is to use regular expressions, and do a simple search/replace on the whole file using a pretty simple regular expression.
Another is to simply load the entire source file into memory, search using strstr for "shared(", and use e.g. strtok to get the arguments. Copy everything else verbatim to the destination.
Take advantage of the C preprocessor.
Put this at the top of the file
#define shared(x,n) { *var = &(x); *var1 = &(n); }
and run in through cpp. This will include external resources also and replace all macros, but you can simply remove all #something lines from the code, convert using injected preprocessor rules and then re-add them.
By the way, why not a simple macro set in a header file for the developer to include?
A doubt: where do var and var1 come from?
EDIT: corrected as shown by johnchen902
When it comes to preprocessor, I'll do this:
#define shared(x,n) (*var=&(x),*var1=&(n))
Why I think it's better than esseks's answer?
Suppose this situation:
if( someBool )
shared(x,n);
else { /* something else */ }
In esseks's answer it will becomes to:
if( someBool )
{ *var = &x; *var1 = &n; }; // compile error
else { /* something else */ }
And in my answer it will becomes to:
if( someBool )
(*var=&(x),*var1=&(n)); // good!
else { /* something else */ }
I am trying to get a list of DLLs that a given process is using, I am trying to achieve that through VirtualQueryEx. My problem is that it return to me just a partial list of DLLs and not all of them (i can see the list using Process Explorer or using VirtualQuery on the given process).
Here's the code:
char szBuf[MAX_PATH * 100] = { 0 };
PBYTE pb = NULL;
MEMORY_BASIC_INFORMATION mbi;
HANDLE h_process = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, iPID);
while (VirtualQueryEx(h_process, pb, &mbi, sizeof(mbi)) == sizeof(mbi)) {
int nLen;
char szModName[MAX_PATH];
if (mbi.State == MEM_FREE)
mbi.AllocationBase = mbi.BaseAddress;
if ((mbi.AllocationBase == hInstDll) ||
(mbi.AllocationBase != mbi.BaseAddress) ||
(mbi.AllocationBase == NULL)) {
// Do not add the module name to the list
// if any of the following is true:
// 1. If this region contains this DLL
// 2. If this block is NOT the beginning of a region
// 3. If the address is NULL
nLen = 0;
} else {
nLen = GetModuleFileNameA((HINSTANCE) mbi.AllocationBase,
szModName, _countof(szModName));
}
if (nLen > 0) {
wsprintfA(strchr(szBuf, 0), "\n%p-%s",
mbi.AllocationBase, szModName);
}
pb += mbi.RegionSize;
}
I am getting the result on szBuf.
This function is part of a DLL file so that it is harder for me to debug.
Right now the DLL is compiled as x64 binary and i am using it against x64 processes.
P.S i know about EnumProcessModules and i am not using it with a reason (too long:).
GetModuleFileName() only gives you the name for modules loaded in your process, not the other process. It will give you a few hits by accident, the Windows operating system DLLs will get loaded at the same address and will thus have the same module handle value.
You will need to use GetModuleFileNameEx() so you can pass the process handle.
Do note the fundamental flaw with your code as posted, you are not doing anything to ensure that you can safely use VirtualQueryEx() on another process. Which requires that you suspend all its threads so it cannot allocate memory while you are iterating it, the kind of thing a debugger does. Also required for EnumProcessModules. The failure mode is nasty, it is random and it can easily get your loop stuck, iterating the same addresses over and over again. Which is why the CreateToolHelp32Snapshot() function exists, emphasis on "snapshot".
I had an earlier question about integrating Mathematica with functions written in C++.
This is a follow-up question:
If the computation takes too long I'd like to be able to abort it using Evaluation > Abort Evaluation. Which of the technologies suggested in the answers make it possible to have an interruptible C-based extension function? How can "interruptibility" be implemented on the C side?
I need to make my function interruptible in a way which will corrupt neither it, nor the Mathematica kernel (i.e. it should be possible to call the function again from Mathematica after it has been interrupted)
For MathLink - based functions, you will have to do two things (On Windows): use MLAbort to check for aborts, and call MLCallYieldFunction, to yield the processor temporarily. Both are described in the MathLink tutorial by Todd Gayley from way back, available here.
Using the bits from my previous answer, here is an example code to compute the prime numbers (in an inefficient manner, but this is what we need here for an illustration):
code =
"
#include <stdlib.h>
extern void primes(int n);
static void yield(){
MLCallYieldFunction(
MLYieldFunction(stdlink),
stdlink,
(MLYieldParameters)0 );
}
static void abort(){
MLPutFunction(stdlink,\" Abort \",0);
}
void primes(int n){
int i = 0, j=0,prime = 1, *d = (int *)malloc(n*sizeof(int)),ctr = 0;
if(!d) {
abort();
return;
}
for(i=2;!MLAbort && i<=n;i++){
j=2;
prime = 1;
while (!MLAbort && j*j <=i){
if(i % j == 0){
prime = 0;
break;
}
j++;
}
if(prime) d[ctr++] = i;
yield();
}
if(MLAbort){
abort();
goto R1;
}
MLPutFunction(stdlink,\"List\",ctr);
for(i=0; !MLAbort && i < ctr; i++ ){
MLPutInteger(stdlink,d[i]);
yield();
}
if(MLAbort) abort();
R1: free(d);
}
";
and the template:
template =
"
void primes P((int ));
:Begin:
:Function: primes
:Pattern: primes[n_Integer]
:Arguments: { n }
:ArgumentTypes: { Integer }
:ReturnType: Manual
:End:
";
Here is the code to create the program (taken from the previous answer, slightly modified):
Needs["CCompilerDriver`"];
fullCCode = makeMLinkCodeF[code];
projectDir = "C:\\Temp\\MLProject1";
If[! FileExistsQ[projectDir], CreateDirectory[projectDir]]
pname = "primes";
files = MapThread[
Export[FileNameJoin[{projectDir, pname <> #2}], #1,
"String"] &, {{fullCCode, template}, {".c", ".tm"}}];
Now, here we create it:
In[461]:= exe=CreateExecutable[files,pname];
Install[exe]
Out[462]= LinkObject["C:\Users\Archie\AppData\Roaming\Mathematica\SystemFiles\LibraryResources\
Windows-x86-64\primes.exe",161,10]
and use it:
In[464]:= primes[20]
Out[464]= {2,3,5,7,11,13,17,19}
In[465]:= primes[10000000]
Out[465]= $Aborted
In the latter case, I used Alt+"." to abort the computation. Note that this won't work correctly if you do not include a call to yield.
The general ideology is that you have to check for MLAbort and call MLCallYieldFunction for every expensive computation, such as large loops etc. Perhaps, doing that for inner loops like I did above is an overkill though. One thing you could try doing is to factor the boilerplate code away by using the C preprocessor (macros).
Without ever having tried it, it looks like the Expression Packet functionality might work in this way - if your C code goes back and asks mathematica for some more work to do periodically, then hopefully aborting execution on the mathematica side will tell the C code that there is no more work to do.
If you are using LibraryLink to link external C code to the Mathematica kernel, you can use the Library callback function AbortQ to check if an abort is in progress.