merge(3p/git): Merge git upstream at v2.26.2 r/808

1 files changed, 45 insertions, 0 deletions

diff --git a/third_party/git/sigchain.h b/third_party/git/sigchain.h
index 138b20f54b40..8e6bada8928c 100644
--- a/third_party/git/sigchain.h
+++ b/third_party/git/sigchain.h
@@ -1,12 +1,57 @@
 #ifndef SIGCHAIN_H
 #define SIGCHAIN_H
 
+/**
+ * Code often wants to set a signal handler to clean up temporary files or
+ * other work-in-progress when we die unexpectedly. For multiple pieces of
+ * code to do this without conflicting, each piece of code must remember
+ * the old value of the handler and restore it either when:
+ *
+ *   1. The work-in-progress is finished, and the handler is no longer
+ *      necessary. The handler should revert to the original behavior
+ *      (either another handler, SIG_DFL, or SIG_IGN).
+ *
+ *   2. The signal is received. We should then do our cleanup, then chain
+ *      to the next handler (or die if it is SIG_DFL).
+ *
+ * Sigchain is a tiny library for keeping a stack of handlers. Your handler
+ * and installation code should look something like:
+ *
+ * ------------------------------------------
+ *   void clean_foo_on_signal(int sig)
+ *   {
+ * 	  clean_foo();
+ * 	  sigchain_pop(sig);
+ * 	  raise(sig);
+ *   }
+ *
+ *   void other_func()
+ *   {
+ * 	  sigchain_push_common(clean_foo_on_signal);
+ * 	  mess_up_foo();
+ * 	  clean_foo();
+ *   }
+ * ------------------------------------------
+ *
+ */
+
+/**
+ * Handlers are given the typedef of sigchain_fun. This is the same type
+ * that is given to signal() or sigaction(). It is perfectly reasonable to
+ * push SIG_DFL or SIG_IGN onto the stack.
+ */
 typedef void (*sigchain_fun)(int);
 
+/* You can sigchain_push and sigchain_pop individual signals. */
 int sigchain_push(int sig, sigchain_fun f);
 int sigchain_pop(int sig);
 
+/**
+ * push the handler onto the stack for the common signals:
+ * SIGINT, SIGHUP, SIGTERM, SIGQUIT and SIGPIPE.
+ */
 void sigchain_push_common(sigchain_fun f);
+
 void sigchain_pop_common(void);
 
 #endif /* SIGCHAIN_H */