Add more examples of locking.

text/examples/barrier/barrier.cc

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+// Copyright Microsoft and CHERIoT
+// Contributors.
+// SPDX-License-Identifier: MIT
+
+#include <atomic>
+#include <stdio.h>
+#include <thread.h>
+
+// entry#begin
+/// Thread entry point.
+__cheri_compartment(
+  "barrier") void entry()
+{
+	static std::atomic<uint32_t>
+	  barrier = 2;
+	printf(
+	  "Thread: %d arrived at barrier\n",
+	  thread_id_get());
+	uint32_t value = --barrier;
+	if (value == 0)
+	{
+		barrier.notify_all();
+	}
+	else
+	{
+		while (value != 0)
+		{
+			barrier.wait(value);
+			value = barrier;
+		}
+	}
+	printf(
+	  "Thread: %d passed barrier\n",
+	  thread_id_get());
+}
+// entry#end

text/examples/barrier/xmake.lua

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+-- Copyright Microsoft and CHERIoT Contributors.
+-- SPDX-License-Identifier: MIT
+
+set_project("CHERIoT example")
+
+sdkdir = os.getenv("CHERIOT_SDK") or
+	"../../../rtos-source/sdk/"
+includes(sdkdir)
+
+set_toolchains("cheriot-clang")
+
+option("board")
+    set_default("sail")
+
+-- An single compartment for this example.
+compartment("barrier")
+    add_files("barrier.cc")
+
+
+-- firmware#begin
+-- Firmware image for the example.
+firmware("barrier_thread")
+    -- RTOS-provided libraries
+    add_deps("freestanding", "stdio")
+    -- Our compartments
+    add_deps("barrier")
+    on_load(function(target)
+        -- The board to target
+        target:values_set("board", "$(board)")
+        -- threads#begin
+        -- Threads to select
+        target:values_set("threads", {
+            {
+                compartment = "barrier",
+                priority = 1,
+                entry_point = "entry",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            },
+            {
+                compartment = "barrier",
+                priority = 2,
+                entry_point = "entry",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            }
+        }, {expand = false})
+        -- threads#end
+    end)
+-- firmware#end

text/examples/locking/locking.cc

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+// Copyright Microsoft and CHERIoT
+// Contributors.
+// SPDX-License-Identifier: MIT
+
+#include <locks.hh>
+#include <stdio.h>
+#include <thread.h>
+
+// declare#begin
+// Comment out this line and uncomment
+// the next one to see how ticket locks
+// behave.
+FlagLock lock;
+// TicketLock lock;
+// declare#end
+
+/**
+ * Function that serves as a placeholder
+ * for something that does work with the
+ * lock held.
+ */
+void do_useful_work()
+{
+	Timeout t{MS_TO_TICKS(1000)};
+	thread_sleep(
+	  &t, ThreadSleepNoEarlyWake);
+}
+
+// low#begin
+__cheri_compartment(
+  "locking") void low()
+{
+	while (true)
+	{
+		lock.lock();
+		printf("Low priority thread "
+		       "acquired lock\n");
+		do_useful_work();
+		lock.unlock();
+	}
+}
+// low#end
+
+// medium#begin
+__cheri_compartment(
+  "locking") void medium()
+{
+	while (true)
+	{
+		lock.lock();
+		printf("Medium priority thread "
+		       "acquired lock\n");
+		do_useful_work();
+		lock.unlock();
+	}
+}
+// medium#end
+
+// high#begin
+__cheri_compartment(
+  "locking") void high()
+{
+	while (true)
+	{
+		lock.lock();
+		printf("High priority thread "
+		       "acquired lock\n");
+		do_useful_work();
+		lock.unlock();
+	}
+}
+// high#end

text/examples/locking/xmake.lua

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+-- Copyright Microsoft and CHERIoT Contributors.
+-- SPDX-License-Identifier: MIT
+
+set_project("CHERIoT example")
+
+sdkdir = os.getenv("CHERIOT_SDK") or
+	"../../../rtos-source/sdk/"
+includes(sdkdir)
+
+set_toolchains("cheriot-clang")
+
+option("board")
+    set_default("sail")
+
+-- An single compartment for this example.
+compartment("locking")
+    add_files("locking.cc")
+
+
+-- firmware#begin
+-- Firmware image for the example.
+firmware("locking_thread")
+    -- RTOS-provided libraries
+    add_deps("freestanding", "stdio")
+    -- Our compartments
+    add_deps("locking")
+    on_load(function(target)
+        -- The board to target
+        target:values_set("board", "$(board)")
+        -- threads#begin
+        -- Threads to select
+        target:values_set("threads", {
+            {
+                compartment = "locking",
+                priority = 1,
+                entry_point = "low",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            },
+            {
+                compartment = "locking",
+                priority = 2,
+                entry_point = "medium",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            },
+            {
+                compartment = "locking",
+                priority = 3,
+                entry_point = "high",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            }
+        }, {expand = false})
+        -- threads#end
+    end)
+-- firmware#end

text/examples/priority_inheritance/priority_inheritance.cc

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+// Copyright Microsoft and CHERIoT
+// Contributors.
+// SPDX-License-Identifier: MIT
+
+#include <locks.hh>
+#include <stdio.h>
+#include <thread.h>
+
+// Comment this line and uncomment the
+// line below to fix the priority
+// inversion in this example.
+FlagLock lock;
+//FlagLockPriorityInherited lock;
+
+// high#begin
+__cheri_compartment(
+  "priority_"
+  "inheritance") void high()
+{
+	// Let the low and
+	// medium-priority threads start
+	Timeout t(MS_TO_TICKS(1000));
+	thread_sleep(&t);
+	while (true)
+	{
+		t = Timeout(MS_TO_TICKS(1000));
+		if (LockGuard g{lock, &t})
+		{
+			printf(
+			  "High-priority thread "
+			  "acquired the lock!\n");
+		}
+		else
+		{
+			printf(
+			  "High-priority thread "
+			  "failed to acquire the "
+			  "lock!\n");
+		}
+	}
+}
+// high#end
+
+std::atomic<int> x;
+
+// medium#begin
+__cheri_compartment(
+  "priority_"
+  "inheritance") void medium()
+{
+	// Let the low-priority thread run
+	// until it yields
+	Timeout t(MS_TO_TICKS(1000));
+	thread_sleep(&t);
+	printf("Medium priority thread "
+	       "entering infinite loop and "
+	       "not yielding\n");
+	while (true)
+	{
+		x++;
+	}
+}
+// medium#end
+
+// low#begin
+__cheri_compartment(
+  "priority_"
+  "inheritance") void low()
+{
+	while (true)
+	{
+		lock.lock();
+		printf("Low-priority thread "
+		       "acquired the lock\n");
+		Timeout t(MS_TO_TICKS(500));
+		thread_sleep(
+		  &t, ThreadSleepNoEarlyWake);
+		printf("Low-priority thread "
+		       "releasing the lock\n");
+		lock.unlock();
+	}
+}
+// low#end

text/examples/priority_inheritance/xmake.lua

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+-- Copyright Microsoft and CHERIoT Contributors.
+-- SPDX-License-Identifier: MIT
+
+set_project("CHERIoT example")
+
+sdkdir = os.getenv("CHERIOT_SDK") or
+	"../../../rtos-source/sdk/"
+includes(sdkdir)
+
+set_toolchains("cheriot-clang")
+
+option("board")
+    set_default("sail")
+
+-- An single compartment for this example.
+compartment("priority_inheritance")
+    add_files("priority_inheritance.cc")
+
+
+-- firmware#begin
+-- Firmware image for the example.
+firmware("priority_inheritance_thread")
+    -- RTOS-provided libraries
+    add_deps("freestanding", "stdio")
+    -- Our compartments
+    add_deps("priority_inheritance")
+    on_load(function(target)
+        -- The board to target
+        target:values_set("board", "$(board)")
+        -- threads#begin
+        -- Threads to select
+        target:values_set("threads", {
+            {
+                compartment = "priority_inheritance",
+                priority = 1,
+                entry_point = "low",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            },
+            {
+                compartment = "priority_inheritance",
+                priority = 2,
+                entry_point = "medium",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            },
+            {
+                compartment = "priority_inheritance",
+                priority = 3,
+                entry_point = "high",
+                stack_size = 0x400,
+                trusted_stack_frames = 2
+            }
+        }, {expand = false})
+        -- threads#end
+    end)
+-- firmware#end