如何進行基于linuxthreads2.0.1線程源碼分析cancel.c

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cancel.c實現了線程的是否可取消，取消類型，取消線程，設置線程退出時需要執行的函數列表等功能。

   
     
 
    
    

/* Thread cancellation */

#include <errno.h>
#include "pthread.h"
#include "internals.h"
#include "restart.h"

/*
 修改線程的可取消屬性。有一個取消點
 取消狀態分為可取消，不可取消
    不可取消的時候，收到取消信號，忽略
    可取消的時候，收到取消信號的時候，根據取消類型做處理。
      立即處理
      不立刻處理，到下一個取消點，判定線程的狀態的取消類型再處理
 */
int pthread_setcancelstate(int state, int * oldstate)
{
  pthread_t self = thread_self();
  if (state < PTHREAD_CANCEL_ENABLE || state > PTHREAD_CANCEL_DISABLE)
    return EINVAL;
  // 保存舊的狀態
  if (oldstate != NULL) *oldstate = self->p_cancelstate;
  // 設置新的狀態
  self->p_cancelstate = state;
  // 判斷線程是否被取消了，并且當前被設置成可取消狀態，并且是需要馬上處理的,則直接退出
  if (self->p_canceled &&
      self->p_cancelstate == PTHREAD_CANCEL_ENABLE &&
      self->p_canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
    pthread_exit(PTHREAD_CANCELED);
  return 0;
}
// 見上一個函數
int pthread_setcanceltype(int type, int * oldtype)
{
  pthread_t self = thread_self();
  if (type < PTHREAD_CANCEL_DEFERRED || type > PTHREAD_CANCEL_ASYNCHRONOUS)
    return EINVAL;
  if (oldtype != NULL) *oldtype = self->p_canceltype;
  self->p_canceltype = type;
  if (self->p_canceled &&
      self->p_cancelstate == PTHREAD_CANCEL_ENABLE &&
      self->p_canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
    pthread_exit(PTHREAD_CANCELED);
  return 0;
}
// 給線程發送取消請求，線程收到該信號是否處理，怎么處理取決于線程本身對于取消的相關配置
int pthread_cancel(pthread_t thread)
{
  thread->p_canceled = 1;
  kill(thread->p_pid, PTHREAD_SIG_CANCEL);
  return 0;
}
// 設置一個取消點
void pthread_testcancel(void)
{
  pthread_t self = thread_self();
  // 判斷線程是不是已經被取消，并且是可取消的，則退出
  if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE)
    pthread_exit(PTHREAD_CANCELED);
}
// 鏈表中新增一個clean函數
void _pthread_cleanup_push(struct _pthread_cleanup_buffer * buffer,
			   void (*routine)(void *), void * arg)
{
  pthread_t self = thread_self();
  buffer->routine = routine;
  buffer->arg = arg;
  // 頭插法
  buffer->prev = self->p_cleanup;
  self->p_cleanup = buffer;
}
// 刪除一個clean節點，execute判斷是否需要執行
void _pthread_cleanup_pop(struct _pthread_cleanup_buffer * buffer,
			  int execute)
{
  pthread_t self = thread_self();
  if (execute) buffer->routine(buffer->arg);
  self->p_cleanup = buffer->prev;
}
// 新增一個clean節點，保存舊的取消類型，設置新的取消類型為PTHREAD_CANCEL_DEFERRED
void _pthread_cleanup_push_defer(struct _pthread_cleanup_buffer * buffer,
				 void (*routine)(void *), void * arg)
{
  pthread_t self = thread_self();
  buffer->routine = routine;
  buffer->arg = arg;
  buffer->canceltype = self->p_canceltype;
  buffer->prev = self->p_cleanup;
  self->p_canceltype = PTHREAD_CANCEL_DEFERRED;
  self->p_cleanup = buffer;
}

// 和上面的函數配套。刪除一個clean節點，execute控制是否需要執行刪除的這個節點，恢復線程的取消類型，是一個有取消點的函數
void _pthread_cleanup_pop_restore(struct _pthread_cleanup_buffer * buffer,
				  int execute)
{
  pthread_t self = thread_self();
  if (execute) buffer->routine(buffer->arg);
  self->p_cleanup = buffer->prev;
  self->p_canceltype = buffer->canceltype;
  if (self->p_canceled &&
      self->p_cancelstate == PTHREAD_CANCEL_ENABLE &&
      self->p_canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
    pthread_exit(PTHREAD_CANCELED);
}
// 線程退出的時候(pthread_exit)調用執行clean鏈表的節點
void __pthread_perform_cleanup(void)
{
  pthread_t self = thread_self();
  struct _pthread_cleanup_buffer * c;
  for (c = self->p_cleanup; c != NULL; c = c->prev) c->routine(c->arg);
}

#ifndef PIC
/* We need a hook to force the cancelation wrappers to be linked in when
   static libpthread is used.  */
extern const int __pthread_provide_wrappers;
static const int * const __pthread_require_wrappers =
  &__pthread_provide_wrappers;
#endif
   

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