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windows: make uv_spawn not fail under job control

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* Fix a potential issue introduced with 415f4d3, namely that uv_spawn
  can fail when the current process is under job control. This would
  happen on Windows versions that don't support nested jobs (versions
  prior to Windows 8 / Server 2012).

* Change the `uv__init_global_job_handle` function signature to match
  what `uv_once` expects.

* Add a bunch of comments that clarify how we're using job control,
  and how we're dealing with job control that might be established by
  our parent process.
This commit is contained in:
Bert Belder 2013-05-16 21:29:40 +02:00
parent 13496e9c1a
commit 4f61ab2058
1 changed files with 42 additions and 3 deletions
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45
src/win/process.c
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@ -49,7 +49,22 @@ static HANDLE uv_global_job_handle_;
static uv_once_t uv_global_job_handle_init_guard_ = UV_ONCE_INIT;
static void uv__init_global_job_handle() {
static void uv__init_global_job_handle(void) {
/* Create a job object and set it up to kill all contained processes when
* it's closed. Since this handle is made non-inheritable and we're not
* giving it to anyone, we're the only process holding a reference to it.
* That means that if this process exits it is closed and all the processes
* it contains are killed. All processes created with uv_spawn that are not
* spawned with the UV_PROCESS_DETACHED flag are assigned to this job.
*
* We're setting the JOB_OBJECT_LIMIT_SILENT_BREAKAWAY_OK flag so only the
* processes that we explicitly add are affected, and *their* subprocesses
* are not. This ensures that our child processes are not limited in their
* ability to use job control on Windows versions that don't deal with
* nested jobs (prior to Windows 8 / Server 2012). It also lets our child
* processes created detached processes without explicitly breaking away
* from job control (which uv_spawn doesn't, either).
*/
SECURITY_ATTRIBUTES attr;
JOBOBJECT_EXTENDED_LIMIT_INFORMATION info;
@ -920,7 +935,18 @@ int uv_spawn(uv_loop_t* loop, uv_process_t* process,
}
process_flags = CREATE_UNICODE_ENVIRONMENT;
if (options.flags & UV_PROCESS_DETACHED) {
/* Note that we're not setting the CREATE_BREAKAWAY_FROM_JOB flag. That
* means that libuv might not let you create a fully deamonized process
* when run under job control. However the type of job control that libuv
* itself creates doesn't trickle down to subprocesses so they can still
* daemonize.
*
* A reason to not do this is that CREATE_BREAKAWAY_FROM_JOB makes the
* CreateProcess call fail if we're under job control that doesn't allow
* breakaway.
*/
process_flags |= DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP;
}
@ -943,8 +969,21 @@ int uv_spawn(uv_loop_t* loop, uv_process_t* process,
if (!(options.flags & UV_PROCESS_DETACHED)) {
uv_once(&uv_global_job_handle_init_guard_, uv__init_global_job_handle);
if (!AssignProcessToJobObject(uv_global_job_handle_, info.hProcess))
uv_fatal_error(GetLastError(), "AssignProcessToJobObject");
if (!AssignProcessToJobObject(uv_global_job_handle_, info.hProcess)) {
/* AssignProcessToJobObject might fail if this process is under job
* control and the job doesn't have the
* JOB_OBJECT_LIMIT_SILENT_BREAKAWAY_OK flag set, on a Windows version
* that doesn't support nested jobs.
*
* When that happens we just swallow the error and continue without
* establishing a kill-child-on-parent-exit relationship, otherwise
* there would be no way for libuv applications run under job control
* to spawn processes at all.
*/
DWORD err = GetLastError();
if (err != ERROR_ACCESS_DENIED)
uv_fatal_error(err, "AssignProcessToJobObject");
}
}
/* Set IPC pid to all IPC pipes. */