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forkfd: Restore errno on exit from the SIGCHLD handler

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I'd never thought about it, but it is a requirement: a signal handler
must leave the global state as it found it (except for those bits that
it intended to change, and those must be done in an async-signal-safe
way). Otherwise, errno could change from one line to the next in the
middle of some code.

[ChangeLog][QtCore][QProcess] On Unix, the QProcess SIGCHLD handler now
restores errno on exit.

Task-number: QTBUG-68472
Change-Id: If025d476890745368955fffd1531e7126f1436d9
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
This commit is contained in:
Thiago Macieira 2018-05-25 10:43:34 -03:00
parent b9dc4f7a96
commit 28ab81158f
1 changed files with 46 additions and 41 deletions
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87
src/3rdparty/forkfd/forkfd.c vendored
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@ -283,6 +283,7 @@ static void notifyAndFreeInfo(Header *header, ProcessInfo *entry,
freeInfo(header, entry);
}
static void reapChildProcesses();
static void sigchld_handler(int signum, siginfo_t *handler_info, void *handler_context)
{
/*
@ -307,19 +308,25 @@ static void sigchld_handler(int signum, siginfo_t *handler_info, void *handler_c
}
if (ffd_atomic_load(&forkfd_status, FFD_ATOMIC_RELAXED) == 1) {
/* is this one of our children? */
BigArray *array;
siginfo_t info;
struct pipe_payload payload;
int i;
int saved_errno = errno;
reapChildProcesses();
errno = saved_errno;
}
}
memset(&info, 0, sizeof info);
memset(&payload, 0, sizeof payload);
static inline void reapChildProcesses()
{
/* is this one of our children? */
BigArray *array;
siginfo_t info;
struct pipe_payload payload;
int i;
memset(&info, 0, sizeof info);
memset(&payload, 0, sizeof payload);
#ifdef HAVE_WAITID
if (!waitid_works)
goto search_arrays;
if (waitid_works) {
/* be optimistic: try to see if we can get the child that exited */
search_next_child:
/* waitid returns -1 ECHILD if there are no further children at all;
@ -371,12 +378,34 @@ search_next_child:
* belongs to one of the chained SIGCHLD handlers. However, there might be another
* child that exited and does belong to us, so we need to check each one individually.
*/
search_arrays:
}
#endif
for (i = 0; i < (int)sizeofarray(children.entries); ++i) {
int pid = ffd_atomic_load(&children.entries[i].pid, FFD_ATOMIC_ACQUIRE);
for (i = 0; i < (int)sizeofarray(children.entries); ++i) {
int pid = ffd_atomic_load(&children.entries[i].pid, FFD_ATOMIC_ACQUIRE);
if (pid <= 0)
continue;
#ifdef HAVE_WAITID
if (waitid_works) {
/* The child might have been reaped by the block above in another thread,
* so first check if it's ready and, if it is, lock it */
if (!isChildReady(pid, &info) ||
!ffd_atomic_compare_exchange(&children.entries[i].pid, &pid, -1,
FFD_ATOMIC_RELAXED, FFD_ATOMIC_RELAXED))
continue;
}
#endif
if (tryReaping(pid, &payload)) {
/* this is our child, send notification and free up this entry */
notifyAndFreeInfo(&children.header, &children.entries[i], &payload);
}
}
/* try the arrays */
array = ffd_atomic_load(&children.header.nextArray, FFD_ATOMIC_ACQUIRE);
while (array != NULL) {
for (i = 0; i < (int)sizeofarray(array->entries); ++i) {
int pid = ffd_atomic_load(&array->entries[i].pid, FFD_ATOMIC_ACQUIRE);
if (pid <= 0)
continue;
#ifdef HAVE_WAITID
@ -384,42 +413,18 @@ search_arrays:
/* The child might have been reaped by the block above in another thread,
* so first check if it's ready and, if it is, lock it */
if (!isChildReady(pid, &info) ||
!ffd_atomic_compare_exchange(&children.entries[i].pid, &pid, -1,
!ffd_atomic_compare_exchange(&array->entries[i].pid, &pid, -1,
FFD_ATOMIC_RELAXED, FFD_ATOMIC_RELAXED))
continue;
}
#endif
if (tryReaping(pid, &payload)) {
/* this is our child, send notification and free up this entry */
notifyAndFreeInfo(&children.header, &children.entries[i], &payload);
notifyAndFreeInfo(&array->header, &array->entries[i], &payload);
}
}
/* try the arrays */
array = ffd_atomic_load(&children.header.nextArray, FFD_ATOMIC_ACQUIRE);
while (array != NULL) {
for (i = 0; i < (int)sizeofarray(array->entries); ++i) {
int pid = ffd_atomic_load(&array->entries[i].pid, FFD_ATOMIC_ACQUIRE);
if (pid <= 0)
continue;
#ifdef HAVE_WAITID
if (waitid_works) {
/* The child might have been reaped by the block above in another thread,
* so first check if it's ready and, if it is, lock it */
if (!isChildReady(pid, &info) ||
!ffd_atomic_compare_exchange(&array->entries[i].pid, &pid, -1,
FFD_ATOMIC_RELAXED, FFD_ATOMIC_RELAXED))
continue;
}
#endif
if (tryReaping(pid, &payload)) {
/* this is our child, send notification and free up this entry */
notifyAndFreeInfo(&array->header, &array->entries[i], &payload);
}
}
array = ffd_atomic_load(&array->header.nextArray, FFD_ATOMIC_ACQUIRE);
}
array = ffd_atomic_load(&array->header.nextArray, FFD_ATOMIC_ACQUIRE);
}
}