core: properly handle fiber cancellation for fiber.cond

Before this patch fiber.cond():wait() just returns for cancelled
fiber. In contrast fiber.channel():get() threw "fiber is
canceled" error.
This patch unify behaviour of channels and condvars and also fixes
related net.box module problem - it was impossible to interrupt
net.box call with fiber.cancel because it used fiber.cond under
the hood. Test cases for both bugs are added.

Closes #4834
Closes #5013

@TarantoolBot document
Title: fiber.cond():wait() throws if fiber is cancelled

Currently fiber.cond():wait() throws an error if waiting fiber is
cancelled like in case with fiber.channel():get().

src/lib/core/fiber_cond.c

@@ -108,6 +108,10 @@ fiber_cond_wait_timeout(struct fiber_cond *c, double timeout)
 		diag_set(TimedOut);
 		return -1;
 	}
+	if (fiber_is_cancelled()) {
+		diag_set(FiberIsCancelled);
+		return -1;
+	}
 	return 0;
 }
 

test/app/gh-5013-fiber_cond-cancel.result

@@ -0,0 +1,46 @@
+-- test-run result file version 2
+fiber = require('fiber')
+ | ---
+ | ...
+test_run = require('test_run').new()
+ | ---
+ | ...
+
+err = nil
+ | ---
+ | ...
+
+test_run:cmd("setopt delimiter ';'")
+ | ---
+ | - true
+ | ...
+function test()
+    _, err = pcall(function() fiber.cond():wait() end)
+end;
+ | ---
+ | ...
+test_run:cmd("setopt delimiter ''");
+ | ---
+ | - true
+ | ...
+
+f = fiber.new(test)
+ | ---
+ | ...
+fiber.yield()
+ | ---
+ | ...
+f:cancel()
+ | ---
+ | ...
+fiber.yield()
+ | ---
+ | ...
+f
+ | ---
+ | - the fiber is dead
+ | ...
+err
+ | ---
+ | - fiber is cancelled
+ | ...

test/app/gh-5013-fiber_cond-cancel.test.lua

@@ -0,0 +1,17 @@
+fiber = require('fiber')
+test_run = require('test_run').new()
+
+err = nil
+
+test_run:cmd("setopt delimiter ';'")
+function test()
+    _, err = pcall(function() fiber.cond():wait() end)
+end;
+test_run:cmd("setopt delimiter ''");
+
+f = fiber.new(test)
+fiber.yield()
+f:cancel()
+fiber.yield()
+f
+err

test/box/net.box_fiber_cancel_gh-4834.result

@@ -0,0 +1,65 @@
+-- test-run result file version 2
+remote = require 'net.box'
+ | ---
+ | ...
+fiber = require 'fiber'
+ | ---
+ | ...
+test_run = require('test_run').new()
+ | ---
+ | ...
+
+-- #4834: Cancelling fiber doesn't interrupt netbox operations
+function infinite_call() fiber.channel(1):get() end
+ | ---
+ | ...
+box.schema.func.create('infinite_call')
+ | ---
+ | ...
+box.schema.user.grant('guest', 'execute', 'function', 'infinite_call')
+ | ---
+ | ...
+
+error_msg = nil
+ | ---
+ | ...
+test_run:cmd("setopt delimiter ';'")
+ | ---
+ | - true
+ | ...
+function gh4834()
+    local cn = remote.connect(box.cfg.listen)
+    local f = fiber.new(function()
+        _, error_msg = pcall(cn.call, cn, 'infinite_call')
+    end)
+    f:set_joinable(true)
+    fiber.yield()
+    f:cancel()
+    f:join()
+    cn:close()
+end;
+ | ---
+ | ...
+test_run:cmd("setopt delimiter ''");
+ | ---
+ | - true
+ | ...
+gh4834()
+ | ---
+ | ...
+error_msg
+ | ---
+ | - fiber is cancelled
+ | ...
+box.schema.func.drop('infinite_call')
+ | ---
+ | ...
+infinite_call = nil
+ | ---
+ | ...
+channel = nil
+ | ---
+ | ...
+error_msg = nil
+ | ---
+ | ...

test/box/net.box_fiber_cancel_gh-4834.test.lua

@@ -0,0 +1,29 @@
+remote = require 'net.box'
+fiber = require 'fiber'
+test_run = require('test_run').new()
+
+-- #4834: Cancelling fiber doesn't interrupt netbox operations
+function infinite_call() fiber.channel(1):get() end
+box.schema.func.create('infinite_call')
+box.schema.user.grant('guest', 'execute', 'function', 'infinite_call')
+
+error_msg = nil
+test_run:cmd("setopt delimiter ';'")
+function gh4834()
+    local cn = remote.connect(box.cfg.listen)
+    local f = fiber.new(function()
+        _, error_msg = pcall(cn.call, cn, 'infinite_call')
+    end)
+    f:set_joinable(true)
+    fiber.yield()
+    f:cancel()
+    f:join()
+    cn:close()
+end;
+test_run:cmd("setopt delimiter ''");
+gh4834()
+error_msg
+box.schema.func.drop('infinite_call')
+infinite_call = nil
+channel = nil
+error_msg = nil