I wrote a simple application to test memory consumption. In this test application, I created four processes to continually consume memory, those processes won't release the memory unless the process exits.
I expected this test application to consume the most memory of RAM and cause the other application to slow down or crash. But the result is not the same as expected. Below is the code:
#include <stdio.h>
#include <unistd.h>
#include <list>
#include <vector>
using namespace std;
unsigned short calcrc(unsigned char *ptr, int count)
{
unsigned short crc;
unsigned char i;
//high cpu-consumption code
//implements the CRC algorithm
//CRC is Cyclic Redundancy Code
}
void* ForkChild(void* param){
vector<unsigned char*> MemoryVector;
pid_t PID = fork();
if (PID > 0){
const int TEN_MEGA = 10 * 10 * 1024 * 1024;
unsigned char* buffer = NULL;
while(1){
buffer = NULL;
buffer = new unsigned char [TEN_MEGA];
if (buffer){
try{
calcrc(buffer, TEN_MEGA);
MemoryVector.push_back(buffer);
} catch(...){
printf("An error was throwed, but caught by our app!\n");
delete [] buffer;
buffer = NULL;
}
}
else{
printf("no memory to allocate!\n");
try{
if (MemoryVector.size()){
buffer = MemoryVector[0];
calcrc(buffer, TEN_MEGA);
buffer = NULL;
} else {
printf("no memory ever allocated for this Process!\n");
continue;
}
} catch(...){
printf("An error was throwed -- branch 2,"
"but caught by our app!\n");
buffer = NULL;
}
}
} //while(1)
} else if (PID == 0){
} else {
perror("fork error");
}
return NULL;
}
int main(){
int children = 4;
while(--children >= 0){
ForkChild(NULL);
};
while(1) sleep(1);
printf("exiting main process\n");
return 0;
}
TOP command
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 2775 steve 20 0 1503m 508 312 R 99.5 0.0 1:00.46 test 2777 steve 20 0 1503m 508 312 R 96.9 0.0 1:00.54 test 2774 steve 20 0 1503m 904 708 R 96.6 0.0 0:59.92 test 2776 steve 20 0 1503m 508 312 R 96.2 0.0 1:00.57 test
Though CPU is high, but memory percent remains 0.0. How can it be possible??
Free command
free shared buffers cached Mem: 3083796 0 55996 428296
Free memory is more than 3G out of 4G RAM.
Does there anybody know why this test app just doesn't work as expected?