Linux 2.6内核下线程模型的改变

Linux内核2.6引入了新的线程模型，除了管理线程的能力大大提高，对于线程分组等管理方式也发生了改变，线程已经成为真正意义上的线程，线程用于了自己ID.(这种线程库好像是 Native Posix Thread Library 即NPTL)

下面这段代码在linux2.4和linux2.6上产生不同的结果：

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#include
#include
#include
#include
#include
#include
#include
#include
#include

static inline _syscall0(int,gettid)

void task1(int *counter);
void task2(int *counter);
void cleanup(int counter1, int counter2);

int g1 = 0;
int g2 = 0;

int main(void) {

 printf("PID = %d \n", getpid());
 printf("PPID = %d \n", getppid());

 pthread_t thrd1, thrd2;
 int ret;

 ret = pthread_create(&thrd1, NULL, (void*(*)(void*))task1, (void*)&g1);
 if (ret) {
  perror("pthread_create: task1");
  exit(EXIT_FAILURE);
 }

 ret = pthread_create(&thrd2, NULL, (void*(*)(void*))task2, (void*)&g2);
 if (ret) {
  perror("pthread_create: task2");
  exit(EXIT_FAILURE);
 }

 printf("threads created: [%d, %d]\n", thrd1, thrd2);

 pthread_join(thrd2, NULL);
 pthread_join(thrd1, NULL);

 cleanup(g1, g2);
 exit(EXIT_SUCCESS);
}

void task1(int *counter) {
 printf("TASK1 PID = %d \n", getpid());
 printf("TASK1 PPID = %d \n", getppid());
 printf("TASK1 thread ID = %d \n", gettid());
 while (*counter < 5) {
  printf("task1 count: %d\n", *counter);
  (*counter)++;
  sleep(1);
 }
}

void task2(int *counter) {
 printf("TASK2 PID = %d \n", getpid());
 printf("TASK2 PPID = %d \n", getppid());
 printf("TASK1 thread ID = %d \n", gettid());

 while (*counter < 5) {
  printf("task2 count: %d\n", *counter);
  (*counter)++;
  sleep(1);
 }
}

void cleanup(int counter1, int counter2)
{
 int i;

 printf("total iterations: %d\n", counter1 + counter2);
}

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在2。4下面的运行结果：

PID = 9862
PPID = 846
threads created: [8194, 16387]
TASK1 PID = 9864
TASK1 PPID = 9863
TASK1 thread ID = 9864
task1 count: 0
TASK2 PID = 9865
TASK2 PPID = 9863
TASK1 thread ID = 9865
task2 count: 0
task1 count: 1
task2 count: 1
task1 count: 2
task2 count: 2
task1 count: 3
task2 count: 3
task1 count: 4
task2 count: 4
total iterations: 10
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在2.6下的运行结果为：

PID = 30015
PPID = 6786
threads created: [-151106640, -161596496]
TASK1 PID = 30015
TASK1 PPID = 6786
TASK1 thread ID = 30016
task1 count: 0
TASK2 PID = 30015
TASK2 PPID = 6786
TASK1 thread ID = 30017
task2 count: 0
task1 count: 1
task2 count: 1
task1 count: 2
task2 count: 2
task1 count: 3
task2 count: 3
task1 count: 4
task2 count: 4
total iterations: 10
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由此可见，在linux2。6下，同一进程所创建的线程将具有相同的进程ID，但具有不同的线程ID，这样就真正兼容POSIX的线程。对其他平台上程序向linux的移植提供了方便。