multithreading - Double Buffer presenting memory leaks [ANSI C] -

i doing library implement double buffer, basic idea there have buffers, 1 written , other read , swap every time write buffer gets full. having memory leaks time when swapping buffers , getting valgrind:

==4778== thread 2: ==4778== invalid read of size 1 ==4778==    @ 0x804a302: swapbuffer (doublebuffer.c:85) ==4778==    0x804a1fa: setdoublebuffer (doublebuffer.c:39) ==4778==    0x804935c: tempcontrol (t2.c:167) ==4778==    0x4062f6f: start_thread (pthread_create.c:312) ==4778==    0x4163bed: clone (clone.s:129) ==4778==  address 0x4228098 0 bytes after block of size 4,000 alloc'd ==4778==    @ 0x402c109: calloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so) ==4778==    0x804a0ff: build_double_buffer (doublebuffer.c:14) ==4778==    0x8048e49: init (t2.c:56) ==4778==    0x804988a: main (t2.c:299) ==4778==  ==4778== invalid read of size 1 ==4778==    @ 0x804a2e8: swapbuffer (doublebuffer.c:86) ==4778==    0x804a1fa: setdoublebuffer (doublebuffer.c:39) ==4778==    0x804935c: tempcontrol (t2.c:167) ==4778==    0x4062f6f: start_thread (pthread_create.c:312) ==4778==    0x4163bed: clone (clone.s:129) ==4778==  address 0x4228098 0 bytes after block of size 4,000 alloc'd ==4778==    @ 0x402c109: calloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so) ==4778==    0x804a0ff: build_double_buffer (doublebuffer.c:14) ==4778==    0x8048e49: init (t2.c:56) ==4778==    0x804988a: main (t2.c:299) ==4778==  ==4778== invalid write of size 1 ==4778==    @ 0x804a2eb: swapbuffer (doublebuffer.c:86) ==4778==    0x804a1fa: setdoublebuffer (doublebuffer.c:39) ==4778==    0x804935c: tempcontrol (t2.c:167) ==4778==    0x4062f6f: start_thread (pthread_create.c:312) ==4778==    0x4163bed: clone (clone.s:129) ==4778==  address 0x4229068 0 bytes after block of size 4,000 alloc'd ==4778==    @ 0x402c109: calloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so) ==4778==    0x804a11a: build_double_buffer (doublebuffer.c:15) ==4778==    0x8048e49: init (t2.c:56) ==4778==    0x804988a: main (t2.c:299) 

i've been trying make work, can't see doing memory leak not how fix it. code below:

#include<stdlib.h> #include<stdio.h> #include<string.h> #include<pthread.h> #include"data_structures.h"  #define buffer_size 4000      typedef enum {firstbuf, secondbuf} currentbuf;  typedef struct {     char *buffer1;     char *buffer2;     currentbuf current;     int index; } double_buffer;   pthread_cond_t buffer_cheio = pthread_cond_initializer; pthread_cond_t buffer_vazio = pthread_cond_initializer; pthread_mutex_t mutex; double_buffer *build_double_buffer(){     double_buffer *db = (double_buffer *)malloc(sizeof(double_buffer));     db->buffer1 = (char *)calloc(buffer_size, sizeof(char));     db->buffer2 = (char *)calloc(buffer_size, sizeof(char));     db->buffer1[0] = '\0';     db->buffer2[0] = '\0';     db->index = 0;     pthread_mutex_init(&mutex, null);     db->current = firstbuf;     return db; }  void setdoublebuffer(double_buffer *db, char *info){     pthread_mutex_lock(&mutex);     int len = strlen(info)+1;     if(db->index + len > buffer_size){         switch(db->current){             case firstbuf:                 while(db->buffer2[0] != '\0'){                     pthread_cond_wait(&buffer_vazio, &mutex);                 }                 break;             case secondbuf:                 while(db->buffer1[0] != '\0'){                     pthread_cond_wait(&buffer_vazio, &mutex);                 }         }         swapbuffer(db);     }     if(db->current == firstbuf){         if(!(db->index + len > buffer_size)){             strcat(db->buffer1, info);         }else{             printf("erro");         }     }else{         if(!(db->index + len > buffer_size)){             strcat(db->buffer2, info);         }else{             printf("erro");         }     }         db->index += len;         pthread_cond_signal(&buffer_cheio);     pthread_mutex_unlock(&mutex); }  void swapbuffer(double_buffer *db){     int i;     char *buf1;     char *buf2;     if(db->current == firstbuf) {         buf1 = db->buffer1;         buf2 = db->buffer2;     } else {         buf2 = db->buffer1;         buf1 = db->buffer2;     }     for(i = 0; < buffer_size -1 || buf1[i] == '\0'; i++){ //line 85         buf2[i] = buf1[i]; //line 86     }     buf1[0] ='\0';     db->index = 0;     if(db->current == firstbuf){         db->current = secondbuf;     }else{         db->current = firstbuf;     } }  void get_buffer(char *receivebuffer, double_buffer *db){     pthread_mutex_lock(&mutex);     int i;     while(db->buffer1[0] == '\0' || db->buffer2[0] == '\0'){         pthread_cond_wait(&buffer_cheio, &mutex);     }     if(db->current == firstbuf){         for(i = 0; < buffer_size || db->buffer2[i] == '\0'; i++){             receivebuffer[i] = db->buffer2[i];         }         db->buffer2[0] = '\0';     }else{         for(i = 0; < buffer_size || db->buffer1[i] == '\0'; i++){             receivebuffer[i] = db->buffer1[i];         }         db->buffer1[0] = '\0';     }     pthread_cond_signal(&buffer_vazio);     pthread_mutex_unlock(&mutex); } 

the code calls is:

//main thread before creating threads log_buffer = build_double_buffer(); //temparature thread while(1){     char *log_string = null;     log_string = (char *)malloc(sizeof(char)*max_buffer_size);      //code calculates t      sprintf(log_string, "temperura: %f\n", t);     setdoublebuffer(log_buffer, log_string); }