6 files changed, 139 insertions, 2 deletions
diff --git a/src/init/lib/esemaphore.c b/src/init/lib/esemaphore.c
new file mode 100644
index 0000000..ac65b02
--- /dev/null
+++ b/src/init/lib/esemaphore.c
@@ -0,0 +1,55 @@
+#include <init/lib/esemaphore.h>
+#include <init/stdlib.h>
+#include <shared/flags.h>
+#include <shared/syscalls.h>
+
+void esem_signal(struct evil_sem *sem) {
+	_syscall_write(sem->signal, NULL, 0, 0);
+}
+
+void esem_wait(struct evil_sem *sem) {
+	_syscall_read(sem->wait, NULL, 0, 0);
+}
+
+struct evil_sem *esem_new(int value) {
+	handle_t ends_wait[2], ends_signal[2];
+	struct evil_sem *sem;
+
+	if (value < 0) return NULL;
+	if (_syscall_pipe(ends_wait, 0) < 0) return NULL;
+	if (_syscall_pipe(ends_signal, 0) < 0) goto fail_signal;
+	if (!(sem = malloc(sizeof *sem))) goto fail_malloc;
+
+	if (!_syscall_fork(FORK_NOREAP, NULL)) {
+		_syscall_close(ends_signal[1]);
+		while (_syscall_read(ends_signal[0], NULL, 0, 0) >= 0) {
+			if (!_syscall_fork(FORK_NOREAP, NULL)) {
+				_syscall_write(ends_wait[1], NULL, 0, 0);
+				_syscall_exit(0);
+			}
+		}
+		_syscall_exit(0);
+	}
+	_syscall_close(ends_signal[0]);
+	_syscall_close(ends_wait[1]);
+
+	sem->wait = ends_wait[0];
+	sem->signal = ends_signal[1];
+
+	while (value--) esem_signal(sem);
+	return sem;
+
+fail_malloc:
+	_syscall_close(ends_signal[0]);
+	_syscall_close(ends_signal[1]);
+fail_signal:
+	_syscall_close(ends_wait[0]);
+	_syscall_close(ends_wait[1]);
+	return NULL;
+}
+
+void esem_free(struct evil_sem *sem) {
+	_syscall_close(sem->wait);
+	_syscall_close(sem->signal);
+	free(sem);
+}
diff --git a/src/init/lib/esemaphore.h b/src/init/lib/esemaphore.h
new file mode 100644
index 0000000..e746bd7
--- /dev/null
+++ b/src/init/lib/esemaphore.h
@@ -0,0 +1,12 @@
+#pragma once
+#include <shared/types.h>
+
+struct evil_sem {
+	handle_t wait, signal;
+};
+
+void esem_signal(struct evil_sem *sem);
+void esem_wait(struct evil_sem *sem);
+
+struct evil_sem *esem_new(int value);
+void esem_free(struct evil_sem *sem);
diff --git a/src/init/tests/main.c b/src/init/tests/main.c
index f0845fe..9adb50c 100644
--- a/src/init/tests/main.c
+++ b/src/init/tests/main.c
@@ -146,5 +146,6 @@ void test_all(void) {
 	run_forked(test_memflag);
 	run_forked(test_malloc);
 	run_forked(test_pipe);
+	run_forked(test_semaphore);
 	run_forked(test_misc);
 }
diff --git a/src/init/tests/main.h b/src/init/tests/main.h
index 47c2507..ed11c5e 100644
--- a/src/init/tests/main.h
+++ b/src/init/tests/main.h
@@ -4,6 +4,7 @@ void stress_all(void);
 void test_all(void);
 
 void test_pipe(void);
+void test_semaphore(void);
 
 #ifdef TEST_MACROS
 
diff --git a/src/init/tests/pipe.c b/src/init/tests/pipe.c
index a980cb8..8e9d243 100644
--- a/src/init/tests/pipe.c
+++ b/src/init/tests/pipe.c
@@ -113,6 +113,4 @@ void test_pipe(void) {
 
 	// not a to.do detect when all processes that can read are stuck on writing to the pipe and vice versa
 	// it seems like linux just lets the process hang endlessly.
-
-	// TODO kill process that's waiting on a pipe
 }
diff --git a/src/init/tests/semaphore.c b/src/init/tests/semaphore.c
new file mode 100644
index 0000000..e542f0b
--- /dev/null
+++ b/src/init/tests/semaphore.c
@@ -0,0 +1,70 @@
+#define TEST_MACROS
+#include <init/lib/esemaphore.h>
+#include <init/stdlib.h>
+#include <init/tests/main.h>
+#include <shared/flags.h>
+#include <shared/syscalls.h>
+
+static void odd(struct evil_sem *sem1, struct evil_sem *sem2) {
+	printf("1");
+	esem_signal(sem1);
+
+	esem_wait(sem2);
+	printf("3");
+	esem_signal(sem1);
+
+	esem_wait(sem2);
+	printf("5");
+	esem_signal(sem1);
+}
+
+static void even(struct evil_sem *sem1, struct evil_sem *sem2) {
+	esem_wait(sem1);
+	printf("2");
+	esem_signal(sem2);
+
+	esem_wait(sem1);
+	printf("4");
+	esem_signal(sem2);
+
+	esem_wait(sem1);
+	printf("6");
+	esem_signal(sem2);
+}
+
+void test_semaphore(void) {
+	struct evil_sem *sem1, *sem2;
+
+	// TODO pipe-based test
+
+	sem1 = esem_new(0);
+	sem2 = esem_new(0);
+	assert(sem1 && sem2);
+	if (!_syscall_fork(0, NULL)) {
+		odd(sem1, sem2);
+		_syscall_exit(69);
+	} else {
+		even(sem1, sem2);
+		assert(_syscall_await() == 69);
+	}
+	esem_free(sem1);
+	esem_free(sem2);
+
+	printf("\n");
+
+	sem1 = esem_new(0);
+	sem2 = esem_new(0);
+	assert(sem1 && sem2);
+	if (!_syscall_fork(0, NULL)) {
+		even(sem1, sem2);
+		_syscall_exit(69);
+	} else {
+		odd(sem1, sem2);
+		assert(_syscall_await() == 69);
+		_syscall_await();
+	}
+	esem_free(sem1);
+	esem_free(sem2);
+
+	printf("\n");
+}