diff options
Diffstat (limited to 'Src')
| -rw-r--r-- | Src/Modules/curses.c | 48 |
1 files changed, 44 insertions, 4 deletions
diff --git a/Src/Modules/curses.c b/Src/Modules/curses.c index 29e088c70..f201847f6 100644 --- a/Src/Modules/curses.c +++ b/Src/Modules/curses.c @@ -1069,8 +1069,47 @@ zccmd_input(const char *nam, char **args) } #endif + /* + * Some documentation for wgetch() says: + + The behavior of getch and friends in the presence of handled signals + is unspecified in the SVr4 and XSI Curses documentation. Under his- + torical curses implementations, it varied depending on whether the + operating system's implementation of handled signal receipt interrupts + a read(2) call in progress or not, and also (in some implementations) + depending on whether an input timeout or non-blocking mode has been + set. + + Programmers concerned about portability should be prepared for either + of two cases: (a) signal receipt does not interrupt getch; (b) signal + receipt interrupts getch and causes it to return ERR with errno set to + EINTR. Under the ncurses implementation, handled signals never inter- + rupt getch. + + * The observed behavior, however, is different: wgetch() consistently + * returns ERR with EINTR when a signal is handled by the shell "trap" + * command mechanism. Further, it consistently returns ERR twice, the + * second time without even attempting to repeat the interrupted read, + * which has the side-effect of NOT updating errno. A third call will + * then begin reading again. + * + * Therefore, to properly implement signal trapping, we must (1) call + * wgetch() in a loop as long as errno remains EINTR, and (2) clear + * errno only before beginning the loop, not on every pass. + * + * There remains a potential bug here in that, if the caller has set + * a timeout for the read [see zccmd_timeout()] the countdown is very + * likely restarted on every call to wgetch(), so an interrupted call + * might wait much longer than desired. + */ + errno = 0; + #ifdef HAVE_WGET_WCH - switch (wget_wch(w->win, &wi)) { + while ((ret = wget_wch(w->win, &wi)) == ERR) { + if (errno != EINTR) + break; + } + switch (ret) { case OK: ret = wctomb(instr, (wchar_t)wi); if (ret == 0) { @@ -1092,9 +1131,10 @@ zccmd_input(const char *nam, char **args) return 1; } #else - ci = wgetch(w->win); - if (ci == ERR) - return 1; + while ((ci = wgetch(w->win)) == ERR) { + if (errno != EINTR) + return 1; + } if (ci >= 256) { keypadnum = ci; *instr = '\0'; |