c - pthread_mutex_lock 卡住了

Question

相关代码可以在这里找到:http://pastebin.com/VbhtQckm
问题出在线上85。 pthread_mutex_lock(ID_retrieval_pool->info->lock);

我正在运行服务器，但它被锁定。内存已分配，我正在初始化互斥锁，它是唯一拥有该共享内存的线程。
我使用 helgrind 工具对 GDB 和 Valgrind 进行了调试，但没有找到任何线索。认为可能导致此问题的可能问题:

• 互斥体未初始化(我使用的 block 是共享内存，我将其初始化为互斥体)；
• 陷入僵局？在手册页中 https://www.sourceware.org/pthreads-win32/manual/pthread_mutex_init.html 说这可能会导致此问题；

请注意，此代码用于学习目的。

编辑，代码为:

// common_header.h + common_header.c
#ifndef DATA_TYPES_H
#define DATA_TYPES_H

#include <pthread.h>
#include <errno.h>

#define RETREIVE_ID_KEY 1

typedef enum {
  SHM_State_None,
  SHM_State_ID_Available,
  SHM_State_ID_Not_Available,
} SHM_State;

typedef struct {
    pthread_mutex_t *lock; // locked if any thread is modifying data
    SHM_State state;
} data_state;

typedef int shmid_t;

typedef struct data_pool {
    data_state *info;
    shmid_t shm_id;
} data_pool;

// other data structures

extern data_state * data_state_initialize_by_setting_address(void *address)
{
  data_state *data = (data_state *)address;
  data->lock = (pthread_mutex_t *)address;
  pthread_mutex_init(data->lock, NULL);
  data->state = SHM_State_None;

  return data;
}
extern data_pool * data_pool_initialize_by_setting_address(void *address)
{
  data_pool *data = (data_pool *)address;
  data->info = data_state_initialize_by_setting_address(address);
  data->shm_id = 0; // invalid though, the structure's client has to set a valid one

  return data;
}
// other initialization functions

#endif // DATA_TYPES_H

///----------------------------------------------------------------------------------------\\\

// main.c -- Server
#include "common_header.h"

#define SHM_INVALID_ADDRESS (void *)-1
#define SHMGET_RW_FLAGS 0666
#define SHMAT_RW_FLAGS 0

bool initialize_data();

static data_pool *ID_retrieval_pool = NULL;

int main(int argc, char *argv[])
{
  if (!initialize_data()) {
    return EXIT_FAILURE;
  }
  // Do other stuff

  return EXIT_SUCCESS;
}

bool initialize_data()
{
  // some irrelevant initialization code
  shmid_t shm_ID = shmget(RETREIVE_ID_KEY,
                          sizeof(data_pool),
                          IPC_CREAT | SHMGET_RW_FLAGS);
  void *shm_address = shmat(shm_ID, NULL, SHMAT_RW_FLAGS);
  if (shm_address == SHM_INVALID_ADDRESS) {
    return false;
  }
  ID_retrieval_pool = data_pool_initialize_by_setting_address(shm_address);
  pthread_mutex_lock(ID_retrieval_pool->info->lock);
  ID_retrieval_pool->shm_id = get_shared_ID();
  ID_retrieval_pool->info->state = SHM_State_ID_Available;
  pthread_mutex_unlock(ID_retrieval_pool->info->lock);

  // other initialization code

  return true;
}

Answer 1

您有一种有趣但不正确的初始化互斥体的方法:

data->lock = (pthread_mutex_t *)address; /* address == &data */
pthread_mutex_init(data->lock, NULL);

在您的代码中，address 是外部结构的地址:这实际上并不分配可用的内存块。

我建议您将互斥锁设置为非指针，然后初始化它:

/* In the struct. */
pthread_mutex_t lock;

/* In your function. */
pthread_mutex_init(&data->lock, NULL);