此问题与How to call a function on a thread's creation and exit?类似，但更具体。在另一个多进程共享内存项目中，我使用了__attribute__((constructor))标记的库init例程，每个线程的延迟初始化和robust futexes的组合，以确保资源不会泄漏到共享内存中，即使系统管理员选择使用SIGKILL进程之一。然而，API中的futexs 方式对于我当前的项目来说太重了，甚至一些关于懒惰初始化的指令也是我宁愿避免的。在几个进程中，几百个线程上的库API就会被称为几万亿次（每个API只有几百个指令。）
我猜答案是否定的，但是因为我花了几个小时寻找并没有找到明确的答案我以为我会在这里问它，然后寻找简单答案的下一个人就能找到它更快。
我的目标非常简单：执行一些每线程初始化，因为线程是在多个进程中异步创建的，并且在线程被异步销毁时可以在某些时候执行某些清理。不必立即，它必须最终发生。
参与批判性思维的一些假设性思想：从__attribute __（（构造函数）标记的库init func调用的假设pthread_atclone（）将满足第一个条件。并且futex（）的扩展为了添加类似semop的操作，每个线程的futex_adj值，如果在do_exit（）中为非零，则导致为futex“信号量”设置FUTEX_OWNER_DIED，允许下次清理futex被触动了。
答案 0 :(得分：0)
那么，首先，您应该记录库用户不应该以这样的方式异步终止线程，即它们不会明确地释放属于您的库的资源（关闭句柄，等等），TBH，只是在进程之前完全终止线程终止是一个坏主意。
在使用你的lib时，检测整个进程是否是SIGKILL更难。我目前最好的猜测是，所有希望使用您的库的进程必须先登录，以便将其pid添加到容器中。使用在lib初始化时启动的线程，查询已经使用kill（pid，0）进行了深入研究的pid并进行任何适当的清理。这不是很令人满意，（我讨厌民意调查），但我没有看到任何不太混乱的选择:(
答案 1 :(得分：0)
经过研究和实验，据我所知，我已经提出了目前似乎是“最佳实践”的内容。如果有人知道更好，请发表评论！
对于第一部分，每线程初始化，我无法提出任何直接延迟初始化的替代方案。但是，我确实认为将分支移动到调用者的效率稍高一些，因此新堆栈框架中的流水线操作不会立即遇到有效的不必要分支。所以不要这样：
__thread int tInf = 0;
void
threadDoSomething(void *data)
{
if (!tInf) {
_threadInitInfo(&tInf);
}
/*l
* do Something.
*/
}
此：
__thread int tInf = 0;
#define threadDoSomething(data) (((!tInf)?_threadInitInfo(&tInf):0), \
_threadDoSomething((data)))
void
_threadDoSomething(void *data)
{
/*l
* do Something.
*/
}
评论这个欢迎的（实际上是轻微的）有用性！
对于第二部分，无论异步如何在线程死亡时强有力地执行一些清理，我无法找到任何解决方案，而不是在打开管道的读取端的文件描述符上有一个收割过程epoll_wait（）通过抽象UNIX域套接字地址上的sendmsg（）调用中的SCM_RIGHTS控制消息传递给它。听起来很复杂，但并不是那么糟糕，这是客户方：
/*m
* Client that registers a thread with a server who will do cleanup of a
* shared interprocess object even if the thread dies asynchronously.
*/
#include <sys/socket.h> // socket(), bind(), recvmsg()
#include <sys/syscall.h> // syscall()
#include <sys/un.h> // sockaddr_un
#include <stdint.h> // uint64_t
#include <fcntl.h> // O_CLOEXEC()
#include <malloc.h> // malloc()
#include <stdlib.h> // random()
#include <unistd.h> // close(), usleep()
#include <pthread.h> // pthread_create()
#include <tsteplsrv.h> // Our API.
char iovBuf[] = "SP1"; // 3 char buf to send client type
__thread pid_t cliTid = 0; // per-thread copy of self's Thread ID
/*f
* initClient() is called when we realise we need to lazily initialise
* our thread based on cliTid being zero.
*/
void *
initClient(void *ptr)
{
struct sockaddr_un svAddr;
struct msghdr msg;
struct iovec io;
struct cmsghdr *ctrMsg;
uint64_t ltid; // local 8-byte copy of the tid
int pfds[2], // two fds of our pipe
sfd; // socket fd
/*s
* This union is necessary to ensure that the buffer is aligned such that
* we can read cmsg_{len,level,type} from the cmsghdr without causing an
* alignment fault (SIGBUS.)
*/
union {
struct cmsghdr hdr;
char buf[CMSG_SPACE(sizeof(int))];
} ctrBuf;
pfds[0] = pfds[1] = sfd = -1;
/*l
* Get our Thread ID.
*/
ltid = (uint64_t)(cliTid = syscall(SYS_gettid));
/*l
* Set up an abstract unix domain socket address.
*/
svAddr.sun_family = AF_UNIX;
svAddr.sun_path[0] = '\0';
strcpy(&svAddr.sun_path[1], EPLS_SRV_ADDR);
/*l
* Set up a socket datagram send buffer.
*/
io.iov_base = iovBuf;
io.iov_len = sizeof(iovBuf);
msg.msg_iov = &io;
msg.msg_iovlen = 1;
msg.msg_control = ctrBuf.buf;
msg.msg_controllen = sizeof(ctrBuf);
msg.msg_name = (struct sockaddr *)&svAddr,
msg.msg_namelen = (&svAddr.sun_path[0] - (char *)&svAddr)
+ 1
+ sizeof(EPLS_SRV_ADDR);
/*l
* Set up the control message header to indicate we are sharing a file
* descriptor.
*/
ctrMsg = CMSG_FIRSTHDR(&msg);
ctrMsg->cmsg_len = CMSG_LEN(sizeof(int));
ctrMsg->cmsg_level = SOL_SOCKET;
ctrMsg->cmsg_type = SCM_RIGHTS;
/*l
* Create file descriptors with pipe().
*/
if (-1 == pipe(pfds)) {
printErrMsg("TID: %d pipe() failed", cliTid);
} else {
/*l
* Write our tid to the pipe.
*/
memmove(CMSG_DATA(ctrMsg), &pfds[0], sizeof(int));
if (-1 == write(pfds[1], <id, sizeof(uint64_t))) {
printErrMsg("TID: %d write() failed", cliTid);
} if (-1 == (sfd = socket(AF_UNIX, SOCK_DGRAM, 0))) {
printErrMsg("TID: %d socket() failed", cliTid);
} else if (-1 == sendmsg(sfd, &msg, 0)) {
printErrMsg("TID: %d sendmsg() failed", cliTid);
} else {
printVerbMsg("TID: %d sent write fd %d to server kept read fd %d",
cliTid,
pfds[0],
pfds[1]);
/*l
* Close the read end of the pipe, the server has it now.
*/
close(pfds[0]);
pfds[0] = -1;
}
}
if (-1 != pfds[1]) close(pfds[1]);
if (-1 != pfds[0]) close(pfds[0]);
if (-1 != sfd) close(sfd);
return (void *)0;
}
收割者的代码：
/*m
* Abstract datagram socket listening for FD's from clients.
*/
#include <sys/socket.h> // socket(), bind(), recvmsg()
#include <sys/epoll.h> // epoll_{create,wait}()
#include <sys/un.h> // sockaddr_un
#include <malloc.h> // malloc()
#include <unistd.h> // close()
#include <tsteplsrv.h> // Our API.
/*s
* socket datagram structs for receiving structured messages used to transfer
* fds from our clients.
*/
struct msghdr msg = { 0 };
struct iovec io = { 0 };
char iovBuf[EPLS_MSG_LEN]; // 3 char buf to receive client type
/*s
* This union is necessary to ensure that the buffer is aligned such that
* we can read cmsg_{len,level,type} from the cmsghdr without causing an
* alignment fault (SIGBUS.)
*/
union {
struct cmsghdr hdr;
char buf[CMSG_SPACE(sizeof(int))];
} ctrBuf;
typedef struct _tidFd_t {
struct _tidFd_t *next;
pid_t tid;
int fd;
} tidFd_t;
tidFd_t *tidFdLst = (tidFd_t *)0;
/*f
* Perform some handshaking with a new client and add the file descriptor
* it shared with us to the epoll set.
*/
static void
welcomeClient(int efd, int cfd)
{
uint64_t tid;
tidFd_t *tfd;
struct epoll_event epEv;
tfd = (tidFd_t *)-1;
/*l
* The fd is a pipe and should be readable, and should contain the
* tid of the client.
*/
if (-1 != read(cfd, &tid, sizeof(tid)) && (tfd = malloc(sizeof(*tfd)))) {
tfd->fd = cfd;
tfd->tid = (pid_t)tid;
tfd->next = tidFdLst;
/*l
* Single threaded process, no race condition here.
*/
tidFdLst = tfd;
/*l
* Add the fd to the epoll() set so that we will be woken up with
* an error if the thread dies.
*/
epEv.events = EPOLLIN;
epEv.data.fd = cfd;
if (-1 == epoll_ctl(efd, EPOLL_CTL_ADD, cfd, &epEv)) {
printErrMsg("TID: %ld Could not register fd %d with epoll set",
tid,
cfd);
} else {
printVerbMsg("TID: %ld Registered fd %d with epoll set", tid, cfd);
}
/*l
* Couldn't allocate memory for the new client.
*/
} else if (!tfd) {
printErrMsg("Could not allocate memory for new client");
/*l
* Could not read from the eventfd() file descriptor.
*/
} else {
printErrMsg("Could not read from client file descriptor");
}
}
/*f
* Perform some handshaking with a new client and add the file descriptor
* it shared with us to the epoll set.
*/
static void
processClientEvent(int efd, struct epoll_event *epEv)
{
tidFd_t *tfd, **bLnk;
/*l
* Walk the list of per-tid fd structs.
*/
for (bLnk = &tidFdLst; (tfd = *bLnk); bLnk = &tfd->next)
if (tfd->fd == epEv->data.fd)
break;
if (!tfd) {
printErrMsg("client file descriptor %d not found on the tfd list!",
epEv->data.fd);
/*l
* If we received an EPOLLHUP on the fd, cleanup.
*/
} else if (epEv->events & EPOLLHUP) {
/*l
* Try to remove the tid's pipe fd from the epoll set.
*/
if (-1 == epoll_ctl(efd, EPOLL_CTL_DEL, epEv->data.fd, epEv)) {
printErrMsg("couldn't delete epoll for tid %d", tfd->tid);
/*l
* Do tid cleanup here.
*/
} else {
printVerbMsg("TID: %d closing fd: %d", tfd->tid, epEv->data.fd);
close(epEv->data.fd);
/*l
* Remove the per-tid struct from the list and free it.
*/
*bLnk = tfd->next;
free(tfd);
}
} else {
printVerbMsg("TID: %d Received unexpected epoll event %d",
tfd->tid,
epEv->events);
}
}
/*f
* Create and listen on a datagram socket for eventfd() file descriptors
* from clients.
*/
int
main(int argc, char *argv[])
{
struct sockaddr_un svAddr;
struct cmsghdr *ctrMsg;
struct epoll_event *epEv,
epEvs[EPLS_MAX_EPEVS];
int sfd, efd, cfd, nfds;
sfd = efd = -1;
/*l
* Set up an abstract unix domain socket address.
*/
svAddr.sun_family = AF_UNIX;
svAddr.sun_path[0] = '\0';
strcpy(&svAddr.sun_path[1], EPLS_SRV_ADDR);
/*l
* Set up a socket datagram receive buffer.
*/
io.iov_base = iovBuf; // 3-char buffer to ID client type
io.iov_len = sizeof(iovBuf);
msg.msg_name = (char *)0; // No need for the client addr
msg.msg_namelen = 0;
msg.msg_iov = &io; // single IO vector in the S/G array
msg.msg_iovlen = 1;
msg.msg_control = ctrBuf.buf; // Control message buffer
msg.msg_controllen = sizeof(ctrBuf);
/*l
* Set up an epoll event.
*/
epEv = &epEvs[0];
epEv->events = EPOLLIN;
/*l
* Create a socket to receive datagrams on and register the socket
* with our epoll event.
*/
if (-1 == (epEv->data.fd = sfd = socket(AF_UNIX, SOCK_DGRAM, 0))) {
printErrMsg("socket creation failed");
/*l
* Bind to the abstract address. The pointer math is to portably
* handle weird structure packing _just_in_case_.
*/
} else if (-1 == bind(sfd,
(struct sockaddr *)&svAddr,
(&svAddr.sun_path[0] - (char *)&svAddr)
+ 1
+ sizeof(EPLS_SRV_ADDR))) {
printErrMsg("could not bind address: %s", &svAddr.sun_path[1]);
/*l
* Create an epoll interface. Set CLOEXEC for tidiness in case a thread
* in the server fork()s and exec()s.
*/
} else if (-1 == (efd = epoll_create1(EPOLL_CLOEXEC))) {
printErrMsg("could not create epoll instance");
/*l
* Add our socket fd to the epoll instance.
*/
} else if (-1 == epoll_ctl(efd, EPOLL_CTL_ADD, sfd, epEv)) {
printErrMsg("could not add socket to epoll instance");
/*l
* Loop receiving events on our epoll instance.
*/
} else {
printVerbMsg("server listening on abstract address: %s",
&svAddr.sun_path[1]);
/*l
* Loop forever listening for events on the fds we are interested
* in.
*/
while (-1 != (nfds = epoll_wait(efd, epEvs, EPLS_MAX_EPEVS, -1))) {
/*l
* For each fd with an event, figure out what's up!
*/
do {
/*l
* Transform nfds from a count to an index.
*/
--nfds;
/*l
* If the fd with an event is the listening socket a client
* is trying to send us their eventfd() file descriptor.
*/
if (sfd == epEvs[nfds].data.fd) {
if (EPOLLIN != epEvs[nfds].events) {
printErrMsg("unexpected condition on socket: %d",
epEvs[nfds].events);
nfds = -1;
break;
}
/*l
* Reset the sizes of the receive buffers to their
* actual value; on return they will be set to the
* read value.
*/
io.iov_len = sizeof(iovBuf);
msg.msg_controllen = sizeof(ctrBuf);
/*l
* Receive the waiting message.
*/
if (-1 == recvmsg(sfd, &msg, MSG_CMSG_CLOEXEC)) {
printVerbMsg("failed datagram read on socket");
/*l
* Verify that the message's control buffer contains
* a file descriptor.
*/
} else if ( NULL != (ctrMsg = CMSG_FIRSTHDR(&msg))
&& CMSG_LEN(sizeof(int)) == ctrMsg->cmsg_len
&& SOL_SOCKET == ctrMsg->cmsg_level
&& SCM_RIGHTS == ctrMsg->cmsg_type) {
/*l
* Unpack the file descriptor.
*/
memmove(&cfd, CMSG_DATA(ctrMsg), sizeof(cfd));
printVerbMsg("Received fd %d from client type %c%c%c",
cfd,
((char *)msg.msg_iov->iov_base)[0],
((char *)msg.msg_iov->iov_base)[1],
((char *)msg.msg_iov->iov_base)[2]);
/*l
* Process the incoming file descriptor and add
* it to the epoll() list.
*/
welcomeClient(efd, cfd);
/*l
* Note but ignore incorrectly formed datagrams.
*/
} else {
printVerbMsg("could not extract file descriptor "
"from client's datagram");
}
/*l
* The epoll() event is on one of the file descriptors
* shared with a client, process it.
*/
} else {
processClientEvent(efd, &epEvs[nfds]);
}
} while (nfds);
/*l
* If something happened to our socket break the epoll_wait()
* loop.
*/
if (nfds)
break;
}
}
/*l
* An error occurred, cleanup.
*/
if (-1 != efd)
close(efd);
if (-1 != sfd)
close(sfd);
return -1;
}
起初我尝试使用eventfd（）而不是pipe（），但eventfd文件描述符表示对象而不是连接，因此在客户端代码中关闭fd并不会在收割者中产生EPOLLHUP。如果有人知道更好的替代pipe（），请告诉我！
为了完整性，这里是用于构造抽象地址的#defines：
/*d
* server abstract address.
*/
#define EPLS_SRV_NAM "_abssSrv"
#define EPLS_SRV_VER "0.0.1"
#define EPLS_SRV_ADDR EPLS_SRV_NAM "." EPLS_SRV_NAM
#define EPLS_MSG_LEN 3
#define EPLS_MAX_EPEVS 32
就是这样，希望这对某人有用。