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iOS: bound safe_area()'s boot-path dispatch_sync to avoid a launch deadlock #74

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iOS: bound safe_area()'s boot-path dispatch_sync to avoid a launch deadlock #74

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18 changes: 15 additions & 3 deletions ios/mob_nif.m
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Original file line number Diff line number Diff line change
Expand Up @@ -1827,10 +1827,19 @@ static ERL_NIF_TERM nif_device_keep_awake(ErlNifEnv *env, int argc, const ERL_NI
// ── NIF: safe_area/0 ─────────────────────────────────────────────────────────
// Returns {Top, Right, Bottom, Left} in logical points (not pixels).
// Must read UIWindow.safeAreaInsets on the main thread.

//
// Called from Mob.Screen.init/1 — i.e. on the boot path, before the first
// screen ever mounts. A plain dispatch_sync here is a deadlock risk: if the
// main thread hasn't reached an idle run-loop tick yet (observed during
// scene-attachment on iPad, including the compatibility-mode window an
// iPhone-only app runs in there), this blocks the BEAM boot thread forever —
// the app never finishes launching. Bound the wait and fall back to zero
// insets on timeout: a screen with wrong insets once is a far smaller bug
// than an app that never boots.
static ERL_NIF_TERM nif_safe_area(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]) {
__block UIEdgeInsets insets = UIEdgeInsetsZero;
dispatch_sync(dispatch_get_main_queue(), ^{
dispatch_semaphore_t done = dispatch_semaphore_create(0);
dispatch_async(dispatch_get_main_queue(), ^{
UIWindow *window = nil;
for (UIScene *scene in [UIApplication sharedApplication].connectedScenes) {
if ([scene isKindOfClass:[UIWindowScene class]]) {
Expand All @@ -1841,7 +1850,10 @@ static ERL_NIF_TERM nif_safe_area(ErlNifEnv *env, int argc, const ERL_NIF_TERM a
}
if (window)
insets = window.safeAreaInsets;
dispatch_semaphore_signal(done);
});
dispatch_time_t deadline = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC));
dispatch_semaphore_wait(done, deadline);
return enif_make_tuple4(
env, enif_make_double(env, insets.top), enif_make_double(env, insets.right),
enif_make_double(env, insets.bottom), enif_make_double(env, insets.left));
Expand Down Expand Up @@ -6327,7 +6339,7 @@ static ERL_NIF_TERM nif_vendor_usb_close(ErlNifEnv *env, int argc, const ERL_NIF
{"register_tap", 1, nif_register_tap, 0},
{"clear_taps", 0, nif_clear_taps, 0},
{"exit_app", 0, nif_exit_app, 0},
{"safe_area", 0, nif_safe_area, 0},
{"safe_area", 0, nif_safe_area, ERL_NIF_DIRTY_JOB_IO_BOUND},
{"haptic", 1, nif_haptic, 0},
{"torch", 1, nif_torch, 0},
{"clipboard_put", 1, nif_clipboard_put, 0},
Expand Down
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