Bug in valgrind? or my mistake? - c

Question

So I wrote a toy program for fun, and at the I moment I finished debugging thinking I finally got everything right, the last check with valgrind gave me 2 errors for not freeing 2 blocks of memory. But the error message really does not make sense to me.
==7419== 80 bytes in 1 blocks are definitely lost in loss record 1 of 2
==7419== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7419== by 0x400C77: mj_Malloc (mj.c:19)
==7419== by 0x401761: main (choco.c:93)
==7419==
==7419== 80 bytes in 1 blocks are definitely lost in loss record 2 of 2
==7419== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7419== by 0x400C77: mj_Malloc (mj.c:19)
==7419== by 0x401776: main (choco.c:94)
==7419==
==7419== LEAK SUMMARY:
==7419== definitely lost: 160 bytes in 2 blocks
Line 94 and 93 in main is
mj_Thread *chocolateMakers = mj_Malloc(nMakers * sizeof *chocolateMakers);
mj_Thread *chocolateEaters = mj_Malloc(nEaters * sizeof *chocolateEaters);
which is freed by
mj_Free(chocolateEaters);
mj_Free(chocolateMakers);
mj_Malloc and mj_Free are simple wrappers for error checking. (mj_Free for consistency)
void *mj_Malloc(size_t size) {
void *p = malloc(size);
if (p == NULL) {
mj_Error("heap allocation failed");
}
return p;
}
void mj_Free(void *p) {
free(p);
}
You can see the whole code below if you want.
choco.c
#include "../mj.c"
typedef struct {
int n;
mj_BlockingQueue orderQueue;
mj_BlockingQueue deliveryQueue;
} *ChocolateArgument;
ChocolateArgument ChocolateArgumentCreate(int n, mj_BlockingQueue orderQueue, mj_BlockingQueue deliveryQueue) {
ChocolateArgument this = mj_Malloc(sizeof *this);
this->n = n;
this->orderQueue = orderQueue;
this->deliveryQueue = deliveryQueue;
return this;
}
int MakeChocolates(void *data) {
ChocolateArgument argument = (ChocolateArgument)data;
while (true) {
if (mj_BlockingQueueOut(argument->orderQueue) != NULL) {
printf("chocolate maker %i going home\n", argument->n);
break;
}
int milli = mj_RandomInt(1, 1000);
mj_Sleep(milli);
printf("new chocolate (maker %i, %.3f seconds)\n", argument->n, (double)milli / 1000.0);
int *pMakerNumber = mj_Malloc(sizeof *pMakerNumber);
*pMakerNumber = argument->n;
mj_BlockingQueueIn(argument->deliveryQueue, pMakerNumber);
}
mj_Free(data);
return EXIT_SUCCESS;
}
void HireChocolateMakers(mj_Thread **pMakers, int nMakers, mj_BlockingQueue orderQueue, mj_BlockingQueue deliveryQueue) {
*pMakers = mj_Malloc(nMakers * sizeof **pMakers);
for (int i = 0; i < nMakers; i += 1) {
ChocolateArgument argument = ChocolateArgumentCreate(i + 1, orderQueue, deliveryQueue);
(*pMakers)[i] = mj_ThreadCreate(MakeChocolates, argument);
}
printf("%i chocolate makers hired\n", nMakers);
}
int EatChocolates(void *data) {
ChocolateArgument argument = (ChocolateArgument)data;
int nOrders = mj_RandomInt(1, 10);
for (int i = 0; i < nOrders; i += 1) {
mj_BlockingQueueIn(argument->orderQueue, NULL);
}
printf("chocolate eater %i ordered %i chocolates\n", argument->n, nOrders);
for (int i = 1; i <= nOrders; i += 1) {
int *pMakerNumber = mj_BlockingQueueOut(argument->deliveryQueue);
printf("maker %i -> eater %i (%i / %i)\n", *pMakerNumber, argument->n, i, nOrders);
free(pMakerNumber);
}
printf("chocolate eater %i is satisfied\n", argument->n);
mj_Free(data);
return EXIT_SUCCESS;
}
void OrderChocolates(mj_Thread **pEaters, int nEaters, mj_BlockingQueue orderQueue, mj_BlockingQueue deliveryQueue) {
*pEaters = mj_Malloc(nEaters * sizeof **pEaters);
for (int i = 0; i < nEaters; i += 1) {
ChocolateArgument argument = ChocolateArgumentCreate(i + 1, orderQueue, deliveryQueue);
(*pEaters)[i] = mj_ThreadCreate(EatChocolates, argument);
}
}
void GoHome(mj_Thread *eaters, int nEaters, mj_Thread *makers, int nMakers, mj_BlockingQueue orderQueue) {
for (int i = 0; i < nEaters; i += 1) {
mj_ThreadWait(eaters[i]);
mj_ThreadDelete(eaters[i]);
}
printf("all chocolate eaters are satisfied\n");
for (int i = 0; i < nMakers; i += 1) {
mj_BlockingQueueIn(orderQueue, NULL + 1);
}
for (int i = 0; i < nMakers; i += 1) {
mj_ThreadWait(makers[i]);
mj_ThreadDelete(makers[i]);
}
}
int main(int argc, char **argv) {
if (argc != 3) {
mj_Error("not enough arguments");
}
int nMakers = atoi(argv[1]);
int nEaters = atoi(argv[2]);
mj_RandomSeed();
mj_BlockingQueue orderQueue = mj_BlockingQueueCreate();
mj_BlockingQueue deliveryQueue = mj_BlockingQueueCreate();
mj_Thread *chocolateMakers = mj_Malloc(nMakers * sizeof *chocolateMakers);
mj_Thread *chocolateEaters = mj_Malloc(nEaters * sizeof *chocolateEaters);
HireChocolateMakers(&chocolateMakers, nMakers, orderQueue, deliveryQueue);
OrderChocolates(&chocolateEaters, nEaters, orderQueue, deliveryQueue);
GoHome(chocolateEaters, nEaters, chocolateMakers, nMakers, orderQueue);
mj_BlockingQueueDelete(orderQueue);
mj_BlockingQueueDelete(deliveryQueue);
mj_Free(chocolateEaters);
mj_Free(chocolateMakers);
return 0;
}
mj.c
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <inttypes.h>
#include <limits.h>
#include <math.h>
#include <time.h>
#include <pthread.h>
#include <semaphore.h>
void mj_Error(char *errorMessage) {
fprintf(stderr, "%s\n", errorMessage);
exit(EXIT_FAILURE);
}
void *mj_Malloc(size_t size) {
void *p = malloc(size);
if (p == NULL) {
mj_Error("heap allocation failed");
}
return p;
}
void mj_Free(void *p) {
free(p);
}
typedef struct mj_QueueElement {
void *data;
struct mj_QueueElement *next;
} *mj_QueueElement;
mj_QueueElement mj_QueueElementCreate(void) {
mj_QueueElement this = mj_Malloc(sizeof *this);
return this;
}
void mj_QueueElementDelete(mj_QueueElement this) {
mj_Free(this);
}
typedef struct {
mj_QueueElement first;
mj_QueueElement last;
} *mj_Queue;
mj_Queue mj_QueueCreate(void) {
mj_Queue this = mj_Malloc(sizeof *this);
this->first = mj_QueueElementCreate();
this->last = this->first;
return this;
}
void mj_QueueDelete(mj_Queue this) {
mj_QueueElementDelete(this->first);
mj_Free(this);
}
void mj_QueueIn(mj_Queue this, void *data) {
this->last->data = data;
this->last->next = mj_QueueElementCreate();
this->last = this->last->next;
}
void *mj_QueueOut(mj_Queue this) {
mj_QueueElement temp = this->first;
void *data = temp->data;
this->first = this->first->next;
mj_QueueElementDelete(temp);
return data;
}
typedef pthread_mutex_t *mj_Mutex;
mj_Mutex mj_MutexCreate(void) {
mj_Mutex this = mj_Malloc(sizeof *this);
pthread_mutex_init(this, NULL);
return this;
}
void mj_MutexDelete(mj_Mutex this) {
pthread_mutex_destroy(this);
mj_Free(this);
}
void mj_MutexLock(mj_Mutex this) {
pthread_mutex_lock(this);
}
void mj_MutexUnlock(mj_Mutex this) {
pthread_mutex_unlock(this);
}
typedef sem_t *mj_Semaphore;
mj_Semaphore mj_SemaphoreCreate(int n) {
mj_Semaphore this = mj_Malloc(sizeof *this);
sem_init(this, 0, n);
return this;
}
void mj_SemaphoreDelete(mj_Semaphore this) {
sem_destroy(this);
mj_Free(this);
}
void mj_SemaphoreUp(mj_Semaphore this) {
sem_post(this);
}
void mj_SemaphoreDown(mj_Semaphore this) {
sem_wait(this);
}
typedef struct {
mj_Queue queue;
mj_Mutex inLock;
mj_Mutex outLock;
mj_Semaphore emptyBlocker;
} *mj_BlockingQueue;
mj_BlockingQueue mj_BlockingQueueCreate(void) {
mj_BlockingQueue this = mj_Malloc(sizeof *this);
this->queue = mj_QueueCreate();
this->inLock = mj_MutexCreate();
this->outLock = mj_MutexCreate();
this->emptyBlocker = mj_SemaphoreCreate(0);
return this;
}
void mj_BlockingQueueDelete(mj_BlockingQueue this) {
mj_QueueDelete(this->queue);
mj_MutexDelete(this->inLock);
mj_MutexDelete(this->outLock);
mj_SemaphoreDelete(this->emptyBlocker);
mj_Free(this);
}
void mj_BlockingQueueIn(mj_BlockingQueue this, void *data) {
mj_MutexLock(this->inLock);
mj_QueueIn(this->queue, data);
mj_SemaphoreUp(this->emptyBlocker);
mj_MutexUnlock(this->inLock);
}
void *mj_BlockingQueueOut(mj_BlockingQueue this) {
mj_MutexLock(this->outLock);
mj_SemaphoreDown(this->emptyBlocker);
void *data = mj_QueueOut(this->queue);
mj_MutexUnlock(this->outLock);
return data;
}
typedef pthread_t *mj_Thread;
typedef struct {
int (*function)(void *);
void *argument;
} *mj_ThreadInfo;
mj_ThreadInfo mj_ThreadInfoCreate(int (*function)(void *), void *argument) {
mj_ThreadInfo this = mj_Malloc(sizeof *this);
this->function = function;
this->argument = argument;
return this;
}
void *mj_ThreadFunction(void *data) {
mj_ThreadInfo info = (mj_ThreadInfo)data;
info->function(info->argument);
mj_Free(data);
return NULL;
}
mj_Thread mj_ThreadCreate(int (*function)(void *), void *argument) {
mj_Thread this = mj_Malloc(sizeof *this);
mj_ThreadInfo info = mj_ThreadInfoCreate(function, argument);
if (pthread_create(this, NULL, mj_ThreadFunction, info) != 0) {
mj_Error("failed to create thread");
}
return this;
}
void mj_ThreadDelete(mj_Thread this) {
mj_Free(this);
}
void mj_ThreadWait(mj_Thread this) {
pthread_join(*this, NULL);
}
void mj_Sleep(int milli) {
struct timespec time;
time.tv_sec = milli / 1000;
time.tv_nsec = (milli % 1000) * 1000000;
nanosleep(&time, NULL);
}
uint64_t mj_RandomInt_s;
uint64_t mj_RandomInt_s2;
void mj_RandomSeed(void) {
srand((unsigned)time(NULL));
mj_RandomInt_s = rand() * rand();
mj_RandomInt_s2 = rand() * rand() * rand();
}
int mj_RandomInt(int from, int to) {
if (from > to) {
mj_Error("invalid arguments");
}
uint64_t x = mj_RandomInt_s;
uint64_t y = mj_RandomInt_s2;
mj_RandomInt_s = y;
x ^= x << 23;
x ^= x >> 17;
x ^= y ^ (y >> 26);
mj_RandomInt_s2 = x;
return (int)((x + y) % (uint64_t)(to - from + 1)) + from;
}

Answer 1

You're allocating chocolateMakers twice (line 93 first and line 36 then) and chocolateEaters twice too (line 94 first and line 62 then). In both cases, you're overwriting the pointer resulting of the first allocation with the one resulting of the second allocation. When you free the allocated memory, you're doing it only once, with the pointers of the second allocations. The pointers of the first allocation are lost, the memory allocated is never freed.