pthread:销毁全局静态互斥量 [英] pthread: destroying global static mutex
问题描述
此代码摘自Richard Stevens编写的UNIX环境中的第三版高级编程.这是如何制作getenv()的可重入版本的示例.这里仅出于学习目的对其进行演示.
This code was taken from the 3rd edition of Advanced Programming in the UNIX Environment, written by Richard Stevens. This is an example of how to make a reentrant version of getenv(). It is demostrated here only for a learning purpose.
/* Copyright (c) W.R.Stevens */
#include <string.h>
#include <errno.h>
#include <pthread.h>
#include <stdlib.h>
extern char **environ;
pthread_mutex_t env_mutex;
static pthread_once_t init_done = PTHREAD_ONCE_INIT;
static void
thread_init(void)
{
pthread_mutexattr_t attr;
pthread_mutexattr_init(&attr);
pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
pthread_mutex_init(&env_mutex, &attr);
pthread_mutexattr_destroy(&attr);
}
int
getenv_r(const char *name, char *buf, int buflen)
{
int i, len, olen;
pthread_once(&init_done, thread_init);
len = strlen(name);
pthread_mutex_lock(&env_mutex);
for (i = 0; environ[i] != NULL; i++) {
if ((strncmp(name, environ[i], len) == 0) &&
(environ[i][len] == '=')) {
olen = strlen(&environ[i][len+1]);
if (olen >= buflen) {
pthread_mutex_unlock(&env_mutex);
return(ENOSPC);
}
strcpy(buf, &environ[i][len+1]);
pthread_mutex_unlock(&env_mutex);
return(0);
}
}
pthread_mutex_unlock(&env_mutex);
return(ENOENT);
}
此代码易于理解.但我有个问题.我们从不调用pthread_mutex_destroy()，这意味着退出时可能会发生内存泄漏(我猜这在平台之间可能会有所不同).
This code is easy to understand. I have a question though. We're never calling pthread_mutex_destroy(), which means that there may be a memory leak on exit (I guess it may differ between platforms).
首先想到的是一个人可以使用PTHREAD_MUTEX_INITIALIZER.是否需要pthread_mutex_init()调用?如果否，则无需调用pthread_mutex_destroy().但是，互斥锁将是非递归的.
First thing that comes to mind is that one may use PTHREAD_MUTEX_INITIALIZER. Does it require pthread_mutex_init() call? If no, there is no need to call pthread_mutex_destroy(). However, the mutex will be non-recursive.
可以编写一个简单的C ++类，该类可以销毁析构函数中的互斥量.但是，它不适合仅使用C编译器的任何人(由于使用一个函数，使用C ++编译器似乎是胡说八道).
One could write a simple C++ class that could destroy mutex in destructor. However, it is not suitable for anyone who has only C compiler (and it seems to be a bullshit to use C++ compiler because of one function).
想到的另一件事是特定于编译器的扩展，例如GCC中的__attribute__((destructor))(可能还有clang).但是，它是不可携带的.
The other thing that comes to mind are compiler-specific extensions like __attribute__((destructor)) in GCC (and hopefully clang). However, it is non-portable.
是否可以避免内存泄漏?如果是的话，那该如何在C语言中完成?
Is it possible to avoid a memory leak? If yes, how can that be done in C?
更新
正如David Butenhof撰写的使用POSIX线程编程"中所出现的那样，我们无需销毁PTHREAD_MUTEX_INITIALIZER变体.具有其他属性的互斥锁如何?
UPDATE
As appears in "Programming with POSIX threads" written by David Butenhof, we never need to destroy PTHREAD_MUTEX_INITIALIZER variant. How about mutexes with other attributes?
推荐答案
在进程终止时仍处于活动状态的资源不是内存泄漏，尽管有一些幼稚的工具将其归类.内存泄漏是程序在生命周期中资源需求的不可逆转且无止境的增长，与实际工作集不成比例.
Resources that are still live at process termination are not memory leaks, despite some naive tools classifying them as such. A memory leak is an irreversible and unbounded growth of a program's resource requirements during its lifetime that's disproportionate to the actual working set.
对于每个POSIX(可在其中获得POSIX线程)，在程序终止时，所有本地进程资源将不复存在.无需明确销毁/释放它们，在某些情况下，像您一样，您不能安全地销毁/释放它们，并且不应尝试.
Per POSIX (which is where you get POSIX threads), all process-local resources cease to exist at program termination. There is no need to destroy/free them explicitly, and in some cases, like yours, you cannot safely destroy/free them and you should not try to.
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