From e5997403e61f46f23255becf22ce8e05a4982405 Mon Sep 17 00:00:00 2001
From: =?utf8?q?J=C3=A9r=C3=B4me=20Benoit?= <jerome.benoit@piment-noir.org>
Date: Mon, 26 Feb 2018 23:26:53 +0100
Subject: [PATCH] Add posix semaphore course example code.
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Signed-off-by: Jérôme Benoit <jerome.benoit@piment-noir.org>
---
 .gitignore            |  1 +
 semaphore/Makefile    | 83 +++++++++++++++++++++++++++++++++++++++++++
 semaphore/semaphore.c | 44 +++++++++++++++++++++++
 3 files changed, 128 insertions(+)
 create mode 100644 semaphore/Makefile
 create mode 100644 semaphore/semaphore.c

diff --git a/.gitignore b/.gitignore
index 728eb36..18e9abd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@ philosophe/philosophe
 prodcons/prodcons
 rw/reader/reader
 rw/writer/writer
+semaphore/semaphore
 signal/signaux0
 threads/exemple1
 upipe/upipe
diff --git a/semaphore/Makefile b/semaphore/Makefile
new file mode 100644
index 0000000..12f70af
--- /dev/null
+++ b/semaphore/Makefile
@@ -0,0 +1,83 @@
+# Sample Makefile to build simple project.
+#
+# This Makefile expect all source files (.c) to be at the same level, in the
+# current working directory.
+#
+# It will automatically generate dependencies, compile all files, and produce a
+# binary using the provided name.
+#
+# Set BINARY_NAME to the name of the binary file to build.
+# Set BUILD_TYPE to either debug or release
+#
+# Automatic dependencies code from:
+# http://make.mad-scientist.net/papers/advanced-auto-dependency-generation/#tldr
+BINARY_NAME=semaphore
+BUILD_TYPE=debug
+#BUILD_TYPE=release
+LDLIBS=-lpthread
+
+# ====================================
+# DO NOT CHANGE STUFF BEYOND THIS LINE
+# ====================================
+
+all: $(BINARY_NAME)
+
+CC=gcc
+LD=gcc
+
+WARN_FLAGS = -Wall -Wextra
+STD_FLAG = -std=c11
+
+ifeq ($(BUILD_TYPE),debug)
+BUILDDIR := .build/debug
+DEBUG_FLAG = -g
+DEBUG = 1
+STRIP_FLAG =
+OPTI_FLAG = -O0
+else
+BUILDDIR := .build/release
+DEBUG_FLAG =
+DEBUG = 0
+STRIP_FLAG = -s
+OPTI_FLAG = -O3
+endif
+
+CFLAGS := -DDEBUG=$(DEBUG) $(CFLAGS) $(WARN_FLAGS) $(STD_FLAG) $(OPTI_FLAG) $(DEBUG_FLAG)
+LDFLAGS := $(LDFLAGS) $(STRIP_FLAG)
+
+OBJDIR := $(BUILDDIR)/objs
+$(shell mkdir -p $(OBJDIR))
+
+SRCS=$(wildcard *.c)
+OBJS=$(patsubst %.c,$(OBJDIR)/%.o,$(SRCS))
+
+DEPDIR := $(BUILDDIR)/deps
+$(shell mkdir -p $(DEPDIR))
+DEPFLAGS = -MT $@ -MMD -MP -MF $(DEPDIR)/$*.Td
+POSTCOMPILE = mv -f $(DEPDIR)/$*.Td $(DEPDIR)/$*.d
+
+$(BINARY_NAME): $(OBJS)
+	@echo "[LD ] $@"
+	@$(LD) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
+
+$(OBJDIR)/%.o: %.c $(DEPDIR)/%.d
+	@echo "[C  ] $*"
+	@$(CC) $(DEPFLAGS) $(CFLAGS) -c $< -o $@
+	@$(POSTCOMPILE)
+
+$(DEPDIR)/%.d: ;
+
+.PRECIOUS: $(DEPDIR)/%.d
+
+include $(wildcard $(patsubst %,$(DEPDIR)/%.d,$(basename $(SRCS))))
+
+clean:
+	@echo "[CLN]"
+	-@rm -r $(BUILDDIR)
+	-@rm $(BINARY_NAME)
+
+disassemble: $(BINARY_NAME)
+	objdump -d $< | less
+
+symbols: $(BINARY_NAME)
+	objdump -t $< | sort | less
diff --git a/semaphore/semaphore.c b/semaphore/semaphore.c
new file mode 100644
index 0000000..28eadba
--- /dev/null
+++ b/semaphore/semaphore.c
@@ -0,0 +1,44 @@
+#include <semaphore.h>		// pour les sémaphores
+#include <pthread.h>		// pour pthread_create et pthread_join
+#include <stdio.h>		// pour printf
+
+#define val 1
+sem_t mutex;			// sémaphore
+int var_glob = 0;
+
+void *increment(void *);
+void *decrement(void *);
+
+int main()
+{
+	pthread_t threadA, threadB;
+	sem_init(&mutex, 0, val);	// initialiser mutex
+	printf("ici main : var_glob = %d\n", var_glob);
+	// création d'un thread pour increment
+	pthread_create(&threadA, NULL, increment, NULL);
+	// création d'un thread pour decrement
+	pthread_create(&threadB, NULL, decrement, NULL);
+	// attendre la fin des threads
+	pthread_join(threadA, NULL);
+	pthread_join(threadB, NULL);
+	printf("ici main, fin threads : var_glob =%d \n", var_glob);
+	return 0;
+}
+
+void *decrement(void *nothing)
+{
+	sem_wait(&mutex);	// attendre l'autorisation d'accès
+	var_glob = var_glob - 1;
+	printf("ici sc de decrement: var_glob= %d\n", var_glob);
+	sem_post(&mutex);
+	return (NULL);
+}
+
+void *increment(void *nothing)
+{
+	sem_wait(&mutex);
+	var_glob = var_glob + 1;
+	printf("ici sc de increment: var_glob= %d\n", var_glob);
+	sem_post(&mutex);
+	return (NULL);
+}
-- 
2.34.1