child::terminate() result in ECHILD in on_exit since boost 1.78 including 1.84

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Description

In boost 1.77 the simple program below results in

Child completed with exit code=9, and error code: Success

whereas since boost 1.78 (also tested 1.79, 1.80, 1.83 & 1.84) it results in

Child completed with exit code=-1, and error code: No child processes

Only boost was changed for these tests compiled using gcc 13.2.0, but has been also been confirmed on other Linux systems with kernel version 5.15 and 6.2.9.

Test program

#include <boost/process.hpp>
#include <boost/asio/io_context.hpp>

#include <iostream>

int main() try {
  boost::asio::io_context ctx;
  namespace bp = boost::process;
  auto proc = bp::child(
      bp::argv({"sleep", "5"}),
      ctx, bp::on_exit = [](int exit, const std::error_code &ec) {
      std::cerr << "Child completed with exit code="
                << exit
                << ", and error code: " << ec.message() << '\n';
      });

  proc.terminate();

  // Run to completion
  ctx.run();

} catch (std::exception const &e) {
  std::cerr << "Unexpected exception " << e.what() << '\n';
}

Syscalls

If it help I'm including the resulting syscalls for both cases.

In boost 1.78+ it seems to waitpid()/wait4 a second time. Section extracted here:

...
[pid 1387918] wait4(1387919,  <unfinished ...>
[pid 1387919] +++ killed by SIGKILL +++
<... wait4 resumed>[{WIFSIGNALED(s) && WTERMSIG(s) == SIGKILL}], 0, NULL) = 1387919
...
wait4(1387919, 0x7ffe02136250, WNOHANG, NULL) = -1 ECHILD (No child processes)

boost 1.77 -> OK

$ strace -f -e '!%file,%memory' result/bin/test 
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffc5bd058b0) = -1 EINVAL (Invalid argument)
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\202\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
close(3)                                = 0
arch_prctl(ARCH_SET_FS, 0x7f225d6c6740) = 0
set_tid_address(0x7f225d6c6a10)         = 1388959
set_robust_list(0x7f225d6c6a20, 24)     = 0
rseq(0x7f225d6c7060, 0x20, 0, 0x53053053) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
futex(0x7f225d65e6fc, FUTEX_WAKE_PRIVATE, 2147483647) = 0
getrandom("\x9f\x8c\xa0\xb6\x55\xec\x3d\x08", 8, GRND_NONBLOCK) = 8
eventfd2(0, EFD_CLOEXEC|EFD_NONBLOCK)   = 3
epoll_create1(EPOLL_CLOEXEC)            = 4
timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC) = 5
epoll_ctl(4, EPOLL_CTL_ADD, 3, {events=EPOLLIN|EPOLLERR|EPOLLET, data={u32=37285688, u64=37285688}}) = 0
write(3, "\1\0\0\0\0\0\0\0", 8)         = 8
epoll_ctl(4, EPOLL_CTL_ADD, 5, {events=EPOLLIN|EPOLLERR, data={u32=37285700, u64=37285700}}) = 0
pipe2([6, 7], 0)                        = 0
fcntl(6, F_SETFL, O_RDONLY|O_NONBLOCK)  = 0
fcntl(7, F_SETFL, O_RDONLY|O_NONBLOCK)  = 0
fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
fcntl(7, F_SETFD, FD_CLOEXEC)           = 0
epoll_ctl(4, EPOLL_CTL_ADD, 6, {events=EPOLLIN|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET, data={u32=37285888, u64=37285888}}) = 0
rt_sigaction(SIGCHLD, {sa_handler=0x407a70, sa_mask=~[RTMIN RT_1], sa_flags=SA_RESTORER, sa_restorer=0x7f225d172eb0}, NULL, 8) = 0
pipe2([8, 9], 0)                        = 0
fcntl(9, F_SETFD, FD_CLOEXEC)           = 0
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f225d6c6a10) = 1388960
strace: Process 1388960 attached
[pid 1388959] close(9)                  = 0
[pid 1388960] set_robust_list(0x7f225d6c6a20, 24 <unfinished ...>
[pid 1388959] read(8,  <unfinished ...>
[pid 1388960] <... set_robust_list resumed>) = 0
[pid 1388960] close(8)                  = 0
[pid 1388959] <... read resumed>"", 8)  = 0
[pid 1388959] close(8)                  = 0
[pid 1388959] wait4(1388960, 0x7ffc5bd05754, WNOHANG, NULL) = 0
[pid 1388959] kill(1388960, SIGKILL)    = 0
[pid 1388959] wait4(1388960, 0x7ffc5bd05754, WNOHANG, NULL) = 0
[pid 1388959] epoll_wait(4, [{events=EPOLLIN, data={u32=37285688, u64=37285688}}], 128, 0) = 1
[pid 1388960] +++ killed by SIGKILL +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_KILLED, si_pid=1388960, si_uid=1337, si_status=SIGKILL, si_utime=0, si_stime=0} ---
write(7, "\21\0\0\0", 4)                = 4
rt_sigreturn({mask=[]})                 = 1
wait4(1388960, [{WIFSIGNALED(s) && WTERMSIG(s) == SIGKILL}], WNOHANG, NULL) = 1388960
write(2, "Child completed with exit code=", 31Child completed with exit code=) = 31
write(2, "9", 19)                        = 1
write(2, ", and error code: ", 18, and error code: )      = 18
write(2, "Success", 7Success)                  = 7
write(2, "\n", 1
)                       = 1
epoll_ctl(4, EPOLL_CTL_DEL, 6, 0x7ffc5bd05704) = 0
close(6)                                = 0
close(7)                                = 0
rt_sigaction(SIGCHLD, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f225d172eb0}, NULL, 8) = 0
close(4)                                = 0
close(5)                                = 0
close(3)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++

boost 1.84 -> ECHILD

$ strace -f -e '!%file,%memory' result/bin/test 
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffe02136880) = -1 EINVAL (Invalid argument)
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\202\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
close(3)                                = 0
arch_prctl(ARCH_SET_FS, 0x7ffad927f740) = 0
set_tid_address(0x7ffad927fa10)         = 1387918
set_robust_list(0x7ffad927fa20, 24)     = 0
rseq(0x7ffad9280060, 0x20, 0, 0x53053053) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
futex(0x7ffad925e6fc, FUTEX_WAKE_PRIVATE, 2147483647) = 0
getrandom("\xf2\xaf\x43\xf5\x80\x83\xac\x46", 8, GRND_NONBLOCK) = 8
eventfd2(0, EFD_CLOEXEC|EFD_NONBLOCK)   = 3
epoll_create1(EPOLL_CLOEXEC)            = 4
timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC) = 5
epoll_ctl(4, EPOLL_CTL_ADD, 3, {events=EPOLLIN|EPOLLERR|EPOLLET, data={u32=25309008, u64=25309008}}) = 0
write(3, "\1\0\0\0\0\0\0\0", 8)         = 8
epoll_ctl(4, EPOLL_CTL_ADD, 5, {events=EPOLLIN|EPOLLERR, data={u32=25309020, u64=25309020}}) = 0
pipe2([6, 7], 0)                        = 0
fcntl(6, F_SETFL, O_RDONLY|O_NONBLOCK)  = 0
fcntl(7, F_SETFL, O_RDONLY|O_NONBLOCK)  = 0
fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
fcntl(7, F_SETFD, FD_CLOEXEC)           = 0
epoll_ctl(4, EPOLL_CTL_ADD, 6, {events=EPOLLIN|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET, data={u32=25309200, u64=25309200}}) = 0
rt_sigaction(SIGCHLD, {sa_handler=0x4073f0, sa_mask=~[RTMIN RT_1], sa_flags=SA_RESTORER, sa_restorer=0x7ffad8d72eb0}, NULL, 8) = 0
pipe2([8, 9], 0)                        = 0
fcntl(9, F_SETFD, FD_CLOEXEC)           = 0
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7ffad927fa10) = 1387919
strace: Process 1387919 attached
[pid 1387918] close(9)                  = 0
[pid 1387919] set_robust_list(0x7ffad927fa20, 24 <unfinished ...>
[pid 1387918] read(8,  <unfinished ...>
[pid 1387919] <... set_robust_list resumed>) = 0
[pid 1387919] close(8)                  = 0
[pid 1387918] <... read resumed>"", 8)  = 0
[pid 1387918] close(8)                  = 0
[pid 1387918] wait4(1387919, 0x7ffe02136364, WNOHANG, NULL) = 0
[pid 1387918] wait4(1387919, 0x7ffe021366f4, WNOHANG, NULL) = 0
[pid 1387919] arch_prctl(0x3001 /* ARCH_??? */, 0x7ffda4ad19d0 <unfinished ...>
[pid 1387918] kill(1387919, SIGKILL <unfinished ...>
[pid 1387919] <... arch_prctl resumed>) = -1 EINVAL (Invalid argument)
[pid 1387918] <... kill resumed>)       = 0
[pid 1387918] wait4(1387919,  <unfinished ...>
[pid 1387919] +++ killed by SIGKILL +++
<... wait4 resumed>[{WIFSIGNALED(s) && WTERMSIG(s) == SIGKILL}], 0, NULL) = 1387919
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_KILLED, si_pid=1387919, si_uid=1337, si_status=SIGKILL, si_utime=0, si_stime=0} ---
write(7, "\21\0\0\0", 4)                = 4
rt_sigreturn({mask=[]})                 = 1387919
epoll_wait(4, [{events=EPOLLIN, data={u32=25309008, u64=25309008}}, {events=EPOLLIN, data={u32=25309200, u64=25309200}}], 128, -1) = 2
read(6, "\21\0\0\0", 4)                 = 4
read(6, 0x7ffe0213651c, 4)              = -1 EAGAIN (Resource temporarily unavailable)
epoll_wait(4, [], 128, 0)               = 0
wait4(1387919, 0x7ffe02136250, WNOHANG, NULL) = -1 ECHILD (No child processes)
write(2, "Child completed with exit code=", 31Child completed with exit code=) = 31
write(2, "-1", 2-1)                       = 2
write(2, ", and error code: ", 18, and error code: )      = 18
write(2, "No child processes", 18No child processes)      = 18
write(2, "\n", 1
)                       = 1
epoll_ctl(4, EPOLL_CTL_DEL, 6, 0x7ffe021366c4) = 0
close(6)                                = 0
close(7)                                = 0
rt_sigaction(SIGCHLD, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7ffad8d72eb0}, NULL, 8) = 0
close(4)                                = 0
close(5)                                = 0
close(3)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++