linux - 尝试在没有阅读器的情况下编写时捕获 SIGPIPE

Question

我正在尝试在 Bash 中的两个进程之间实现命名管道通信解决方案。

第一个进程向命名管道写入内容:

send(){
    echo 'something' > $NAMEDPIPE
}

第二个脚本应该像这样读取命名管道:

while true;do
  if read line < $NAMEDPIPE;do
      someCommands
  fi
done

注意之前已经使用传统命令创建了命名管道

mkfifo $NAMEDPIPE

我的问题是读取器脚本并不总是运行，因此如果写入器脚本尝试写入命名管道，它将一直处于阻塞状态，直到读取器连接到管道。

我想避免这种行为，解决方案是捕获 SIGPIPE 信号。事实上，根据 man 7 的说法，当试图在没有阅读器的管道中写入时，应该发送信号。所以我改变了我的红色功能:

read(){
    trap 'echo "SIGPIPE received"' SIGPIPE
    echo 'something' > $NAMEDPIPE
}

但是当我运行阅读器脚本时，脚本保持阻塞状态，并且不会打印“SIGPIPE received”。

我是对信号机制有误解还是有更好的解决方案来解决我的问题？

Answer 1

这是我刚刚制作的一个有趣的代码。也许你可以引用这个:

#!/bin/bash

shopt -s extglob

NAMEDPIPE=/var/run/sr-pipe
RECEIVER_PID_FILE=/var/run/sr-receiver-pid

function sender_start {
    # Create named pipe.

    if [[ -e $NAMEDPIPE ]]; then
        echo "[Sender] Named pipe \"$NAMEDPIPE\" already exists."
    else
        echo "[Sender] Creating named pipe \"$NAMEDPIPE\"."
        mkfifo "$NAMEDPIPE" || {
            echo "Failed to create named pipe \"$NAMEDPIPE\"."
            exit 1
        }
    fi

    # Wait for receiver.

    echo "[Sender] Waiting for receiver."
    local PID
    until [[ -e $RECEIVER_PID_FILE ]] \
    && read PID < "$RECEIVER_PID_FILE" \
    && [[ $PID == +([[:digit:]]) ]] \
    && kill -s 0 "$PID" &>/dev/null; do
        sleep 1s
    done
    echo "[Sender] Receiver is [now] active."

    # Send signal.

    kill -s SIGPIPE "$PID"

    # Send messages.

    local SEND=''

    echo "[Sender] Now sending messages."
    while sleep 1s; do
        SEND=$RANDOM
        echo "[Sender] Sending $SEND."
        echo "$SEND" >&4
    done 4>"$NAMEDPIPE"
}

function receiver_start {
    echo "$BASHPID" > "$RECEIVER_PID_FILE"

    echo "[Receiver] Receiver is now active."

    local QUIT=false RECEIVE=false

    trap 'RECEIVE=true' SIGPIPE
    trap 'QUIT=true' SIGINT SIGTERM SIGHUP

    while [[ $QUIT == false ]]; do
        if [[ $RECEIVE == true ]]; then
            RECEIVE=false
            echo "[Receiver] Now receiving messages."
            while [[ $QUIT == false ]] && IFS= read -r -u 4 LINE; do
                echo "[Receiver] Received $LINE."
            done 4<"$NAMEDPIPE"
        fi
        sleep 1s
    done
}

if [[ $1 == send ]]; then
    sender_start
elif [[ $1 == receive ]]; then
    receiver_start
fi

我在一个终端上运行了这个:

# bash sender-receiver.sh send
[Sender] Named pipe "/var/run/sr-pipe" already exists.
[Sender] Waiting for receiver.
[Sender] Receiver is [now] active.
[Sender] Now sending messages.
[Sender] Sending 21524.
[Sender] Sending 1460.
[Sender] Sending 8352.
[Sender] Sending 4424.
...

在另一个上我得到了这个(更正):

# bash sender-receiver.sh receive
[Receiver] Receiver is now active.
[Receiver] Now receiving messages.
[Receiver] Received 21524.
[Receiver] Received 1460.
[Receiver] Received 8352.
[Receiver] Received 4424.
...

您可能可以在同一终端上在后台运行发送方，在前台运行接收方。