new framework to inhibit thread cancellation when needed

with these small changes, libc functions which need to call functions
which are cancellation points, but which themselves must not be
cancellation points, can use the CANCELPT_INHIBIT and CANCELPT_RESUME
macros to temporarily inhibit all cancellation.

1 files changed, 13 insertions, 3 deletions

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 284b45a0..52487001 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -57,9 +57,19 @@ static void cancel_handler(int sig, siginfo_t *si, void *ctx)
 static void cancelpt(int x)
 {
 	struct pthread *self = __pthread_self();
-	if (self->canceldisable) return;
-	if ((self->cancelpoint+=x)==1 && x>=0 && self->cancel)
-		docancel(self);
+	switch (x) {
+	case 1:
+		self->cancelpoint++;
+	case 0:
+		if (self->cancel && self->cancelpoint==1 && !self->canceldisable)
+			docancel(self);
+		break;
+	case -1:
+		self->cancelpoint--;
+		break;
+	default:
+		self->canceldisable += x;
+	}
 }
 
 /* "rsyscall" is a mechanism by which a thread can synchronously force all