diff options
Diffstat (limited to 'Modules/posixmodule.c')
| -rw-r--r-- | Modules/posixmodule.c | 103 |
1 files changed, 103 insertions, 0 deletions
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c index 607d40b..1d9a33a 100644 --- a/Modules/posixmodule.c +++ b/Modules/posixmodule.c @@ -72,6 +72,8 @@ */ #if defined(__APPLE__) +#include <mach/mach.h> + #if defined(__has_builtin) #if __has_builtin(__builtin_available) #define HAVE_BUILTIN_AVAILABLE 1 @@ -6745,6 +6747,104 @@ os_register_at_fork_impl(PyObject *module, PyObject *before, } #endif /* HAVE_FORK */ +// Common code to raise a warning if we detect there is more than one thread +// running in the process. Best effort, silent if unable to count threads. +// Constraint: Quick. Never overcounts. Never leaves an error set. +// +// This code might do an import, thus acquiring the import lock, which +// PyOS_BeforeFork() also does. As this should only be called from +// the parent process, it is in the same thread so that works. +static void warn_about_fork_with_threads(const char* name) { + // TODO: Consider making an `os` module API to return the current number + // of threads in the process. That'd presumably use this platform code but + // raise an error rather than using the inaccurate fallback. + Py_ssize_t num_python_threads = 0; +#if defined(__APPLE__) && defined(HAVE_GETPID) + mach_port_t macos_self = mach_task_self(); + mach_port_t macos_task; + if (task_for_pid(macos_self, getpid(), &macos_task) == KERN_SUCCESS) { + thread_array_t macos_threads; + mach_msg_type_number_t macos_n_threads; + if (task_threads(macos_task, &macos_threads, + &macos_n_threads) == KERN_SUCCESS) { + num_python_threads = macos_n_threads; + } + } +#elif defined(__linux__) + // Linux /proc/self/stat 20th field is the number of threads. + FILE* proc_stat = fopen("/proc/self/stat", "r"); + if (proc_stat) { + size_t n; + // Size chosen arbitrarily. ~60% more bytes than a 20th column index + // observed on the author's workstation. + char stat_line[160]; + n = fread(&stat_line, 1, 159, proc_stat); + stat_line[n] = '\0'; + fclose(proc_stat); + + char *saveptr = NULL; + char *field = strtok_r(stat_line, " ", &saveptr); + unsigned int idx; + for (idx = 19; idx && field; --idx) { + field = strtok_r(NULL, " ", &saveptr); + } + if (idx == 0 && field) { // found the 20th field + num_python_threads = atoi(field); // 0 on error + } + } +#endif + if (num_python_threads <= 0) { + // Fall back to just the number our threading module knows about. + // An incomplete view of the world, but better than nothing. + PyObject *threading = PyImport_GetModule(&_Py_ID(threading)); + if (!threading) { + PyErr_Clear(); + return; + } + PyObject *threading_active = + PyObject_GetAttr(threading, &_Py_ID(_active)); + if (!threading_active) { + PyErr_Clear(); + Py_DECREF(threading); + return; + } + PyObject *threading_limbo = + PyObject_GetAttr(threading, &_Py_ID(_limbo)); + if (!threading_limbo) { + PyErr_Clear(); + Py_DECREF(threading); + Py_DECREF(threading_active); + return; + } + Py_DECREF(threading); + // Duplicating what threading.active_count() does but without holding + // threading._active_limbo_lock so our count could be inaccurate if + // these dicts are mid-update from another thread. Not a big deal. + // Worst case if someone replaced threading._active or threading._limbo + // with non-dicts, we get -1 from *Length() below and undercount. + // Nobody should, but we're best effort so we clear errors and move on. + num_python_threads = (PyMapping_Length(threading_active) + + PyMapping_Length(threading_limbo)); + PyErr_Clear(); + Py_DECREF(threading_active); + Py_DECREF(threading_limbo); + } + if (num_python_threads > 1) { + PyErr_WarnFormat( + PyExc_DeprecationWarning, 1, +#ifdef HAVE_GETPID + "This process (pid=%d) is multi-threaded, " +#else + "This process is multi-threaded, " +#endif + "use of %s() may lead to deadlocks in the child.", +#ifdef HAVE_GETPID + getpid(), +#endif + name); + PyErr_Clear(); + } +} #ifdef HAVE_FORK1 /*[clinic input] @@ -6771,6 +6871,7 @@ os_fork1_impl(PyObject *module) /* child: this clobbers and resets the import lock. */ PyOS_AfterFork_Child(); } else { + warn_about_fork_with_threads("fork1"); /* parent: release the import lock. */ PyOS_AfterFork_Parent(); } @@ -6810,6 +6911,7 @@ os_fork_impl(PyObject *module) /* child: this clobbers and resets the import lock. */ PyOS_AfterFork_Child(); } else { + warn_about_fork_with_threads("fork"); /* parent: release the import lock. */ PyOS_AfterFork_Parent(); } @@ -7479,6 +7581,7 @@ os_forkpty_impl(PyObject *module) /* child: this clobbers and resets the import lock. */ PyOS_AfterFork_Child(); } else { + warn_about_fork_with_threads("forkpty"); /* parent: release the import lock. */ PyOS_AfterFork_Parent(); } |