signal: Add 'signal block' support

This allows a signal to be blocked by setting it's handler to SIG_IGN

Can be used to block SIGPIPE for exec

Signed-off-by: Steve Bennett <steveb@workware.net.au>

3 files changed, 65 insertions, 24 deletions

diff --git a/jim-signal.c b/jim-signal.c
index cec541a..7d02e68 100644
--- a/jim-signal.c
+++ b/jim-signal.c
@@ -22,7 +22,7 @@
 #endif
 
 static jim_wide *sigloc;
-static jim_wide sigsblocked;
+static jim_wide sigsignored;
 static struct sigaction *sa_old;
 static struct {
     int status;
@@ -34,16 +34,16 @@ static struct {
 
 static void signal_handler(int sig)
 {
-    /* We just remember which signals occurred. Jim_Eval() will
-     * notice this as soon as it can and throw an error
+    /* Remember which signals occurred and store in *sigloc.
+     * Jim_Eval() will notice this as soon as it can and throw an error
      */
     *sigloc |= sig_to_bit(sig);
 }
 
 static void signal_ignorer(int sig)
 {
-    /* We just remember which signals occurred */
-    sigsblocked |= sig_to_bit(sig);
+    /* Remember which signals occurred for access by 'signal check' */
+    sigsignored |= sig_to_bit(sig);
 }
 
 static void signal_init_names(void)
@@ -169,6 +169,7 @@ static int find_signal_by_name(Jim_Interp *interp, const char *name)
 
 #define SIGNAL_ACTION_HANDLE 1
 #define SIGNAL_ACTION_IGNORE -1
+#define SIGNAL_ACTION_BLOCK -2
 #define SIGNAL_ACTION_DEFAULT 0
 
 static int do_signal_cmd(Jim_Interp *interp, int action, int argc, Jim_Obj *const *argv)
@@ -194,9 +195,13 @@ static int do_signal_cmd(Jim_Interp *interp, int action, int argc, Jim_Obj *cons
         if (action == SIGNAL_ACTION_HANDLE) {
             sa.sa_handler = signal_handler;
         }
-        else {
+        else if (action == SIGNAL_ACTION_IGNORE) {
             sa.sa_handler = signal_ignorer;
         }
+        else {
+            /* SIGNAL_ACTION_BLOCK */
+            sa.sa_handler = SIG_IGN;
+        }
     }
 
     /* Iterate through the provided signals */
@@ -209,6 +214,7 @@ static int do_signal_cmd(Jim_Interp *interp, int action, int argc, Jim_Obj *cons
         if (action != siginfo[sig].status) {
             /* Need to change the action for this signal */
             switch (action) {
+                case SIGNAL_ACTION_BLOCK:
                 case SIGNAL_ACTION_HANDLE:
                 case SIGNAL_ACTION_IGNORE:
                     if (siginfo[sig].status == SIGNAL_ACTION_DEFAULT) {
@@ -246,6 +252,11 @@ static int signal_cmd_ignore(Jim_Interp *interp, int argc, Jim_Obj *const *argv)
     return do_signal_cmd(interp, SIGNAL_ACTION_IGNORE, argc, argv);
 }
 
+static int signal_cmd_block(Jim_Interp *interp, int argc, Jim_Obj *const *argv)
+{
+    return do_signal_cmd(interp, SIGNAL_ACTION_BLOCK, argc, argv);
+}
+
 static int signal_cmd_default(Jim_Interp *interp, int argc, Jim_Obj *const *argv)
 {
     return do_signal_cmd(interp, SIGNAL_ACTION_DEFAULT, argc, argv);
@@ -269,7 +280,7 @@ static int signal_cmd_check(Jim_Interp *interp, int argc, Jim_Obj *const *argv)
 {
     int clear = 0;
     jim_wide mask = 0;
-    jim_wide blocked;
+    jim_wide ignored;
 
     if (argc > 0 && Jim_CompareStringImmediate(interp, argv[0], "-clear")) {
         clear++;
@@ -292,17 +303,13 @@ static int signal_cmd_check(Jim_Interp *interp, int argc, Jim_Obj *const *argv)
         mask = ~mask;
     }
 
-    if ((sigsblocked & mask) == 0) {
-        /* No matching signals, so empty result and nothing to do */
-        return JIM_OK;
-    }
     /* Be careful we don't have a race condition where signals are cleared but not returned */
-    blocked = sigsblocked & mask;
+    ignored = sigsignored & mask;
     if (clear) {
-        sigsblocked &= ~blocked;
+        sigsignored &= ~ignored;
     }
     /* Set the result */
-    signal_set_sigmask_result(interp, blocked);
+    signal_set_sigmask_result(interp, ignored);
     return JIM_OK;
 }
 
@@ -316,9 +323,9 @@ static int signal_cmd_throw(Jim_Interp *interp, int argc, Jim_Obj *const *argv)
         }
     }
 
-    /* If the signal is ignored (blocked) ... */
+    /* If the signal is ignored ... */
     if (siginfo[sig].status == SIGNAL_ACTION_IGNORE) {
-        sigsblocked |= sig_to_bit(sig);
+        sigsignored |= sig_to_bit(sig);
         return JIM_OK;
     }
 
@@ -370,6 +377,13 @@ static const jim_subcmd_type signal_command_table[] = {
         -1,
         /* Description: Lists ignored signals, or adds to ignored signals */
     },
+    {   "block",
+        "?signals ...?",
+        signal_cmd_block,
+        0,
+        -1,
+        /* Description: Lists blocked signals, or adds to blocked signals */
+    },
     {   "default",
         "?signals ...?",
         signal_cmd_default,
diff --git a/jim_tcl.txt b/jim_tcl.txt
index 247ad7e..352071e 100644
--- a/jim_tcl.txt
+++ b/jim_tcl.txt
@@ -57,6 +57,7 @@ Changes since 0.78
 1. Add `file mtimeus` for high resolution file timestamps
 2. `aio` now supports datagram Unix-Domain sockets
 3. Add support for `aio lock -wait`
+4. Add `signal block` to prevent delivery of signals
 
 Changes between 0.77 and 0.78
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -3798,8 +3799,16 @@ Commands which return a list of signal names do so using the canonical form:
     `signal check` to determine which signals have occurred but
     been ignored.
 
++*signal block* ?'signals \...'?+::
+    If no signals are given, returns a lists all signals which are currently
+    being blocked.
+    If signals are specified, these are added to the list of signals
+    currently being blocked. These signals are not delivered to the process.
+    This can be useful for signals such as +SIGPIPE+, especially in conjunction
+    with `exec` as child processes inherit the parent's signal disposition.
+
 +*signal default* ?'signals \...'?+::
-    If no signals are given, returns a lists all signals which are currently have
+    If no signals are given, returns a lists all signals which currently have
     the default behaviour.
     If signals are specified, these are added to the list of signals which have
     the default behaviour.
diff --git a/tests/exec2.test b/tests/exec2.test
index 08f3d11..b4b42cc 100644
--- a/tests/exec2.test
+++ b/tests/exec2.test
@@ -5,12 +5,15 @@
 source [file dirname [info script]]/testing.tcl
 
 needs cmd exec
+foreach i {pipe signal wait} {
+	testConstraint $i [expr {[info commands $i] ne ""}]
+}
 # Some Windows platforms (e.g. AppVeyor) produce ENOSPC rather than killing
 # the child with SIGPIPE). So turn off this test for that platform
-if {[info commands pipe] ne "" && [env MSYSTEM ""] ne "MINGW32"} {
-	testConstraint pipe 1
+if {[info exists env(MSYSTEM)] && $env(MSYSTEM) eq "MINGW32"} {
+	testConstraint nomingw32 0
 } else {
-	testConstraint pipe 0
+	testConstraint nomingw32 1
 }
 
 set d \"
@@ -58,7 +61,7 @@ test exec2-3.1 "close pipeline return value" {
 	list $rc $msg $status $exitcode
 } {1 {child process exited abnormally} CHILDSTATUS 1}
 
-test exec2-3.2 "close pipeline return value" -constraints pipe -body {
+test exec2-3.2 "close pipeline return value" -constraints {pipe nomingw32} -body {
 	# Create a pipe and immediately close the read end
 	lassign [pipe] r w
 	close $r
@@ -71,7 +74,23 @@ test exec2-3.2 "close pipeline return value" -constraints pipe -body {
 	list $rc $msg $status $exitcode
 } -match glob -result {1 {child killed*} CHILDKILLED SIGPIPE}
 
-test exec2-3.4 "wait for background task" {
+test exec2-3.3 "close pipeline with SIGPIPE blocked" -constraints {pipe signal nomingw32} -body {
+	# Create a pipe and immediately close the read end
+	lassign [pipe] r w
+	close $r
+	signal block SIGPIPE
+	# Write more than 64KB which is maximum size of the pipe buffers
+	# on all systems we have seen
+	set bigstring [string repeat a 100000]
+	set f [open [list |cat << $bigstring >$@w 2>/dev/null]]
+	set rc [catch {close $f} msg opts]
+	lassign [dict get $opts -errorcode] status pid exitcode
+	list $rc $msg $status $exitcode
+} -match glob -result {1 {child process exited*} CHILDSTATUS 1} -cleanup {
+	signal default SIGPIPE
+}
+
+test exec2-3.4 "wait for background task" -constraints wait -body {
 	set pid [exec sleep 0.1 &]
 	lassign [wait $pid] status newpid exitcode
 	if {$pid != $newpid} {
@@ -79,7 +98,6 @@ test exec2-3.4 "wait for background task" {
 	} else {
 		list $status $exitcode
 	}
-} {CHILDSTATUS 0}
-
+} -result {CHILDSTATUS 0}
 
 testreport