how to invoke global variables in dynamic link library? - c

Question

I have 3 .c source files: common.c, interface_1.c, interface_2.c.
In common.c, I define some functions and global variables, and in interface_1.c and interface_2.c, these functions and global variables will be invoked.
Now, interface_1.c and interface_2.c will be compiled to .dll so as to be used by other program. The problem is that, while two dll files are called, global variables defined in common.c should be the same, which means: if a global variable is changed during the process of calling interface_1.dll, the same variable in interface_2.dll should be changed at the same time.
Background
I want to use PLECS to do power electronics simulation. There is a block called DLL which is very powerful. User can write c/cpp code and compile them to dynamic link library. Each DLL block can only call one .dll file. I have two DLL blocks and want to make a global variable to communicate between them.
The template of c source file which will be compile to dll are shown below.
DllHeader.h
#ifndef PLECSDLLHEADER_H_
#define PLECSDLLHEADER_H_
#if defined _WIN32
#define DLLEXPORT __declspec(dllexport)
#elif __GNUC__ >=4
#define DLLEXPORT __attribute__ ((visibility("default")))
#else
#define DLLEXPORT
#endif
#ifdef __cplusplus
extern "C" {
#endif
#pragma pack(push, 4)
struct SimulationSizes {
int numInputs; /* the number of inputs that the DLL needs */
int numOutputs; /* the number of outputs that the DLL provides */
int numStates; /* the number of discrete states that the DLL needs */
int numParameters; /* the number of user parameters that the DLL needs */
};
struct SimulationState {
const double* const inputs; /* array of input values (read-only) */
double* const outputs; /* array of output values (to fill by DLL) */
double* const states; /* array of discrete states (read/write) */
const double* const parameters; /* array of parameters (read-only) */
const double time; /* current simulation time (read-only) */
const char* errorMessage; /* error message to set by DLL */
void* userData; /* pointer to any DLL data (untouched by PLECS) */
};
#pragma pack(pop)
/* Required: DLL needs to set all fields in aSizes. */
/* Called once before the simulation. */
DLLEXPORT void plecsSetSizes(struct SimulationSizes* aSizes);
/* Optional: DLL may acquire resources, initialize states and outputs. */
/* Called once during the initialization of a new simulation. */
DLLEXPORT void plecsStart(struct SimulationState* aState);
/* Required: DLL needs to set outputs depending on inputs and states. */
/* Called whenever the simulation time reaches a multiple of the sample */
/* time. */
DLLEXPORT void plecsOutput(struct SimulationState* aState);
/* Optional: DLL may release any acquired resources. */
/* Called when the simulation is finished, even when an error occured. */
DLLEXPORT void plecsTerminate(struct SimulationState* aState);
#ifdef __cplusplus
}
#endif
#endif /* PLECSDLLHEADER_H_ */
interface.c
#include "DllHeader.h"
//Map input and output parameters to meaningful names
#define in aState->inputs[0]
#define out aState->outputs[0]
DLLEXPORT void plecsSetSizes(struct SimulationSizes* aSizes)
{
aSizes->numInputs = 1;
aSizes->numOutputs = 1;
aSizes->numStates = 0;
aSizes->numParameters = 0; //number of user parameters passed in
}
//This function is automatically called at the beginning of the simulation
DLLEXPORT void plecsStart(struct SimulationState* aState)
{
// do some initialization ...
}
//This function is automatically called every sample time
//output is written to DLL output port after the output delay
DLLEXPORT void plecsOutput(struct SimulationState* aState)
{
// do some calculation ...
}

Answer 1

Using LoadLibrary works. Be careful that in interface.c full path of common.dll should be specified! Solution is shown at the end.
For Lundin, it's involved in embedded development, some variables are time-based, which means they are alive all the time and invoked by other control functions. For example, a signal is sampled and passed to a variable, this sampled data will be used in several place, such as filter, closed-loop control... So it's difficult to decouple these messy usage...
common.h
#ifndef COMMON_H_
#define COMMON_H_
#if defined _WIN32
#define DLLEXPORT __declspec(dllexport)
#elif __GNUC__ >=4
#define DLLEXPORT __attribute__ ((visibility("default")))
#else
#define DLLEXPORT
#endif
#ifdef __cplusplus
extern "C" {
#endif
#pragma pack(push, 4)
typedef struct{
float a;
float b;
} Coord;
#pragma pack(pop)
extern Coord curPos;
DLLEXPORT Coord GetcurPos(void);
DLLEXPORT float getMax(float a, float b);
DLLEXPORT void SetcurPos(float a, float b);
#ifdef __cplusplus
}
#endif
#endif /* COMMON_H_ */
common.c
#include "common.h"
Coord curPos;
DLLEXPORT float getMax(float a, float b){
return a>b?a:b;
}
DLLEXPORT Coord GetcurPos(void){
return curPos;
}
DLLEXPORT void SetcurPos(float a, float b){
curPos.a=a;
curPos.b=b;
}
interface_a.c
#include "DllHeader.h"
#include <windows.h>
#include "common.h"
//Map input and output parameters to meaningful names
#define in aState->inputs[0]
#define out aState->outputs[0]
HMODULE module;
typedef float(*AddFunc)(float, float);
typedef Coord (*PosGetter)(void);
AddFunc dllmax;
PosGetter getCurPos;
DLLEXPORT void plecsSetSizes(struct SimulationSizes* aSizes)
{
aSizes->numInputs = 1;
aSizes->numOutputs = 1;
aSizes->numStates = 0;
aSizes->numParameters = 0; //number of user parameters passed in
}
DLLEXPORT void plecsStart(struct SimulationState* aState)
{
module = LoadLibrary(TEXT("D:\\Simulation\\PLECSLearn\\DLL\\global_test\\common.dll"));
if (module == NULL)
{
aState->errorMessage = "Failed to load common.dll";
}
dllmax = (AddFunc)GetProcAddress(module, "getMax");
getCurPos = (PosGetter)GetProcAddress(module, "GetcurPos");
}
//This function is automatically called every sample time
//output is written to DLL output port after the output delay
DLLEXPORT void plecsOutput(struct SimulationState* aState)
{
if (getCurPos().a == 1){
out = 2;
} else {
out = -1;
}
// out = dllmax(200,300);
}
interface_b.c
#include "DllHeader.h"
#include <windows.h>
#include "common.h"
//Map input and output parameters to meaningful names
#define in aState->inputs[0]
#define out aState->outputs[0]
HMODULE module;
typedef float(*AddFunc)(float, float);
typedef Coord (*PosGetter)(void);
typedef void (*PosSetter)(float, float);
AddFunc dllmax;
PosGetter getCurPos;
PosSetter setCurPos;
DLLEXPORT void plecsSetSizes(struct SimulationSizes* aSizes)
{
aSizes->numInputs = 1;
aSizes->numOutputs = 1;
aSizes->numStates = 0;
aSizes->numParameters = 0; //number of user parameters passed in
}
DLLEXPORT void plecsStart(struct SimulationState* aState)
{
module = LoadLibrary(TEXT("D:\\Simulation\\PLECSLearn\\DLL\\global_test\\common.dll"));
if (module == NULL)
{
aState->errorMessage = "Failed to load common.dll";
}
dllmax = (AddFunc)GetProcAddress(module, "getMax");
getCurPos = (PosGetter)GetProcAddress(module, "GetcurPos");
setCurPos = (PosSetter)GetProcAddress(module, "SetcurPos");
}
//This function is automatically called every sample time
//output is written to DLL output port after the output delay
DLLEXPORT void plecsOutput(struct SimulationState* aState)
{
static int cnt = 0;
if (cnt<5000){
setCurPos(0,0);
}else{
setCurPos(1,2);
}
cnt++;
out = getCurPos().a;
}