我正在为一些用餐野人问题的变量写一个C解决方案。 现在，我创建线程，每个线程获得一个FILE *到同一个调试文件;在线程内我正在使用fprintf（）进行一些打印。打印的声明不受任何类型的互斥锁保护。
我没有在调试文件中观察到任何交错行为;它似乎是线程安全的，虽然无处在线我发现了一个确定的声明，就是这种情况。
我所看到的是以下内容：
fprintf是线程安全的fprintf需要是线程安全的我之所以要问这是因为这是一项有效的大学任务，但我仍然怀疑在另一台基于Windows的计算机中，由于上面讨论的不确定性，该程序可能会导致问题。
我将附上线程代码，以便您看到prinintg不受保护：
DWORD WINAPI RoomateThread(LPVOID lpParam) {
/*=================================================
"RoomateThread" this is the roomate thread handler function where
the thread logic is implemented
Input: 1. lpParam holds a roomate, runtime and pointers to both files
Output: 1. return an DWORD value {0}->Success {-1}->Failure
2. A code telling if the run was successful (debug file)
A roommate follows this logic after wake up:
1. If there are clothes available in the closet:
a. Wait for mutex to be available, take it
b. Check if the basket is full
b.1. If it is - start the machine and wait for it to finish
c. Throw an item in the basket
d. release mutex
2. If the closet is empty, wait for laundry_is_empty signal, then goto (1.a)
=================================================*/
/*variable declerations*/
DWORD wait_res, delta;
BOOL release_res;
LONG previous_count;
roomate_thread *elem;
elem = (roomate_thread*)lpParam;
/*thread logic*/
while (TRUE) {
/*calculate the delta between the total run time and the time the roomate had run so far*/
delta = total_time - elem->run_time;
/*wait until the minimum between period Ti and delta*/
Sleep(min(elem->roomate->run_time,delta));
fprintf(elem->debug, "RoomateThread(): Line %d, roomate %d: slept for %d mili sec, starting...\n", __LINE__, elem->roomate->roomate_id, min(elem->roomate->run_time, delta));
/*as instructed, each roomate is active since the wakeup*/
fprintf(elem->report, "\nRoomate %d active", elem->roomate->roomate_id);
/*update the element total run time since start*/
elem->run_time = elem->run_time + min(elem->roomate->run_time, delta);
if (time_to_stop < elem->run_time) {
/*if the element total run time is bigger then the global variable update the global*/
time_to_stop = elem->run_time;
}
/*its time to close the thread properly*/
if (time_to_stop == total_time) {
/*if the laundry basket has clothes in it, and the roomate run as much as the total time
activate rhe robot once more and exit*/
if (elem->run_time == total_time && items_in_laundry!=0) {
release_res = ReleaseSemaphore(
laundry_is_full,
1,
&previous_count);
if (release_res == FALSE) {
fprintf(elem->debug, "MachineThread(): Line %d, released semaphore 'laundry_is_full' failed\nthe last error is: 0X%x\n", __LINE__, GetLastError());
return FAILURE;
}
}
break;
}
/*checks that the roomate has clothes in the closet to continue*/
if (elem->roomate->clothes_in_laundry < elem->roomate->clothes-1) {/*roomate has clothes available*/
fprintf(elem->debug, "RoomateThread(): Line %d, roomate id= %d, number of dirty clothes=%d, number of total dirty clothes=%d\n",__LINE__, elem->roomate->roomate_id, elem->roomate->clothes_in_laundry, items_in_laundry);
}
// It's empty:
else {
/*waits until one of the roomates will activate the robot, cause there is no clothes in the roomate closet*/
fprintf(elem->debug, "DAVIDS roomate %d have no clothes, waiting!!!\n", elem->roomate->roomate_id);
elem->roomate->closet_empty = TRUE;
/*Wait until the machine is done*/
wait_res = WaitForSingleObject(laundry_is_empty, INFINITE);
fprintf(elem->debug, "RoomateThread(): Line %d, roomate %d have clothes,finish waiting!!!\n",__LINE__, elem->roomate->roomate_id);
if (wait_res != WAIT_OBJECT_0) {
fprintf(elem->debug, "RoomateThread() error: Line %d, waiting for sempahore 'laundry_is_empty' failed\nthe last error is: 0X%x\n", __LINE__,GetLastError());
return FAILURE;
}
fprintf(elem->debug, "RoomateThread(): Line %d, laundry_is_empty semaphore aquired , roomate: %d\n", __LINE__,elem->roomate->roomate_id);
}
/* Wait for mutex (machine start and clothes add "rights")*/
wait_res = WaitForSingleObject(mutex, INFINITE);
if (wait_res != WAIT_OBJECT_0) {
fprintf(elem->debug, "RoomateThread() error: Line %d, waiting for 'mutex' failed\nthe last error is: 0X%x\n", __LINE__,GetLastError());
return FAILURE;
}
fprintf(elem->debug, "RoomateThread(): Line %d, mutex aquired , roomate: %d\n", __LINE__, elem->roomate->roomate_id);
fprintf(elem->debug, "RoomateThread(): Line 200, mutex aquired , roomate: %d\n",elem->roomate->roomate_id);
/*Check if basket it full*/
if (items_in_laundry == total_items) {
/*Start Machine*/
release_res = ReleaseSemaphore(
laundry_is_full,
1,
&previous_count);
if (release_res == FALSE) {
fprintf(elem->debug, "MachineThread(): Line %d, released semaphore 'laundry_is_empty' failed\nthe last error is: 0X%x\n", __LINE__, GetLastError());
return FAILURE;
}
fprintf(elem->debug, "RoomateThread(): Line 210, released semaphore 'laundry_is_full' last count is: %ld\n", previous_count);
/*Wait for it to finish*/
wait_res = WaitForSingleObject(laundry_is_empty, INFINITE);
if (wait_res != WAIT_OBJECT_0) {
fprintf(elem->debug, "RoomateThread() error: Line %d, waiting for sempahore 'laundry_is_empty' failed\nthe last error is: 0X%x\n", __LINE__, GetLastError());
return FAILURE;
}
items_in_laundry = 0;
}
/*Throw in a dirty cloth*/
elem->roomate->clothes_in_laundry++;
items_in_laundry++;
/*Release the mutex*/
release_res = ReleaseMutex(mutex);
if (release_res == FALSE) {
fprintf(elem->debug, "RoomateThread(): Line %d, released 'mutex' failed\nthe last error is: 0X%x\n", __LINE__, GetLastError());
return FAILURE;
}
fprintf(elem->debug, "RoomateThread(): Line %d, mutex released , roomate: %d\n", __LINE__, elem->roomate->roomate_id);
}
fprintf(elem->debug, "RoomateThread(): Line %d, thread of roomate %d ended\n", __LINE__, elem->roomate->roomate_id);
return SUCSSES;
}
只需重新构建，这将使用visual 2015在Windows上运行
会感激一些帮助!!!
**如果您需要更多代码，我会添加，但其余的不是提问的信息
答案 0 :(得分：3)
C2011 - 首先承认线程存在的标准的第一个版本 - 不限制fprintf()在不同线程中调用的方式可能或确实相互作用。从这个意义上讲，fprintf() 不是线程安全的。
fprintf()调用不会相互干扰，如果它们都指定了相同的目标文件，则它们的输出将不会混合。因此，符合POSIX的fprintf()在这个意义上是线程安全的。
我不能说标准C ++是否存在要求fprintf()具有线程安全性的要求。我会发现这令人惊讶，但它可能是真的。可以肯定的是，从多个线程写入iostream对象是安全的，但这并不意味着fprintf()也是如此。
但是，如果您询问的是Windows C或C ++，那么这一点并不重要，但是，众所周知，C（特别是C）是不合格的。如果您想了解Windows的fprintf()，请that has already been answered here（是）。
答案 1 :(得分：0)
在我看来，输出可能会混杂在一起：
功能：int fprintf（文件*流，常量字符*模板等）
Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe mem lock corrupt | See POSIX Safety Concepts. This function is just like printf, except that the output is written to the stream stream instead of stdout.
和“ MT安全”定义（强调我的意思）：
在出现以下情况时，可以安全地调用MT安全或线程安全功能 其他线程。 MT-Safe中的MT代表多线程。
成为MT-Safe并不意味着功能是原子的，也不意味着它使用POSIX向用户公开的任何内存同步机制。 甚至有可能依次调用MT-Safe功能 不会产生MT安全组合。例如，进行线程调用 两种MT-Safe功能，一个接一个，不保证 等同于两者结合的原子执行的行为 函数，因为其他线程中的并发调用可能会干扰 破坏性的方式。
可以在库中内联函数的整个程序优化 接口可能会暴露不安全的重新排序，因此执行内联 不建议跨GNU C库接口使用。有据可查 在整个程序优化中不能保证MT安全状态。 但是，用户可见标头中定义的功能旨在 可以安全地进行内联。